IME, it varies.

One issue that looms huge in this discussion is generational turnover, and by that I don't principally refer to the supposed preferences of Silents-Boomers-early Xers versus late Xers-Millennials-Zoomers. Rather I principally refer to: the intersection of (a) education (and the lack thereof) x (b) technology.

(a) The ability to read music confidently and the ability to sing or play an instrument with at least a threshold level of skill appears to be far less widespread than it used to (the decline is multi-generational).

(b) The advent of mobile devices that could carry your entire music library, followed by streaming subscriptions, greatly intensified the cultural pattern that music is something heard passively.

Traditional musical idioms/forms that sound good and inviting to join without any need for accompaniment are, in my experience, the best threshold for making it possible for more people to sing. But that doesn't mean people will feel compelled to accept the invitation; it's merely a more plausible invitation.

As for vernacular texts, that can be mixed regardless of traditional vs contempo. For example, in the latter category, there's a fair representation of text choices that raise eyebrows and titters even among people who prefer the contempo idiom; that's a function of insufficient time to sift/winnow that chaff out (what we have kept in repertoire of the older idiom represents the fruit of a much longer sifting/winnowing process that we are largely unaware of). In the traditional category, I would not lead with choosing old texts that could readily come across more as twee than having gravitas.

In practical terms, a few other issues:

1. Pew Catholics (unlike Pew Lutherans, Methodists, Episcopalians and some others) typically avoid what I refer to as "singing naked" - that is, they are shy about hearing themselves sing, and more confident when there are confident singers not too far away from them in the pews. I am a huge believer in not sucking all or most confident singers out of the pews into the choir and in encouraging choristers who are not singing with the choir for divers reasons to seat themselves in the middle to front-of-back of the congregation. On the other hand, said Pew Catholics are much more prone to bow out of singing on all but best known hymns if the instrumental accompaniment (or ampified cantor) is too loud or overbearing; they don't take it as a challenge to match, but as a "why bother?" moment. (That is, shy Pew Catholics want to hear *voices* near them, not instruments overpower them.)

2. Acoustics: not all acoustics are equally suited to congregational singing, musical idioms, and instruments.

3. More subtly - Tempo: the "spaciousness" beloved in some Episcopalian musical traditions is rarely well received/executed among American Pew Catholics. The late great Theodore Marier evinced some well-founded knowledge about this by choosing traditional tune melodies whose verses lines could be sung through by congregations without breath-catch pause or a break in the energy of the line (think of arsis and thesis in chant melodies; Marier certainly did in this regard) so long as the tempo didn't invite sagging or breaks. Not all tunes are equal on this point, but it's worth diagnosing one's choices from this perspective.

When I took my last music position -stayed there 20 years - my predecessor had thrown in new music nearly every other week. The congregation rarely learned anything before it all changed again. Who says the so-called contemporary 70s stuff is easy to sing? It is not. I chose approximately 30 or so traditional hymns that would get us through the liturgical year and work within the limitations of the hymnal. They learned those hymns and sang them well. It just takes a little time and as the previous poster indicated, consistency.

I served for 10 years in a parish for a Sunday evening (last gasp) mass. Because it wasn't in a particularly "good" part of town (there were visible bullet holes in the parish hall), the attendance varied widely according to the seasons. In the dead of winter, we were lucky if we had 30 people. But in the height of summer, sometimes this mass would have 75 or more people.
When I arrived, I took a very conservative approach to hymn selection. If we had to repeat 2 or 3 hymns every Sunday in Advent, or in Lent, I thought it was worth it, because the hymn singing continued to improve. I always soloed out the melody for the introduction, and the intros were not always short!
The pastor was very pleased with what I did. I would add about one "new" hymn every two or three months. I thought I was being adventurous when I scheduled "The Church's One Foundation," but was pleased that they sang it reasonably well. So I scheduled it for three more Sundays, and the confidence increased.
By the end of 10 years, I always had robust singing. It broke my heart that a change of pastors brought all of my hard work to and end. But, the few folks who knew me back then still great me fondly when I attend the parish festival.
I had to remind myself, this was a struggling parish, not a major parish.

I’m struggling with introduction even one new hymn per week of the Easter season. This is all the more problematic without an organ. Some of the tunes are too chromatic even if we had an organ, and they don’t know the texts. There are also not many Paschal Time options; the St John of Damascene texts are explicitly for Easter so I feel a bit discouraged. And that’s looking at the two Episcopal hymnals of the last century, to Liam’s point about the winnowing process.

1. Pew Catholics (unlike Pew Lutherans, Methodists, Episcopalians and some others) typically avoid what I refer to as "singing naked"

Yes and we have some problems. Our 8:30 NO Mass with hymns might as well not have any, and while the phenomenon described means that the organist and lone chorister have full freedom aside from the final Marian antiphon always sung, it’s a bummer that the people hardly sing even carols.

On the other hand I’m going to have to speak to someone in the congregation who sings flat and loudly and sings out of turn on Gregorian hymns that the cantor alone (me) intones at benediction; everyone else understands this. There are written instructions and frankly the possibility of flubbing it was made worse when I realized that I then had to sing over someone.

The late great Theodore Marier evinced some well-founded knowledge about this by choosing traditional tune melodies whose verses lines could be sung through by congregations without breath-catch pause or a break in the energy of the line (think of arsis and thesis in chant melodies; Marier certainly did in this regard) so long as the tempo didn't invite sagging or breaks.

We have never formally had this discussion but we always breathe in time when there’s a question of a breath in a hymn such as Lead kindly light (SANDON) where you need one but it might lead to a pause or sagging tempo if you don’t do it right.

I think it’s pastoral patience: fewer hymns, chosen carefully, sung repeatedly, and allowed to take root. When that happens, congregational singing usually returns

My situation is different because we already have congregational singing. But we have a monthly (or seasonal) hymn: it might change for feasts or special occasions (and it is sometimes the same on feasts: we use the devotional months tied to feasts as a guide sometimes). But we use it multiple times a month. I now add a different hymn each week after Vespers to build our repertoire. For example we did Jerusalem the Golden to AURELIA (more reusable than EWING, and I love the tune) for Laetare.

I hope to go approximately every other week within a year.

Oh, and while we are considering possibly unnecessary obstacles to singing-shy Pew Catholics: key/pitch and whether the shape of a melodic line invites or discourages participation by such singers. What works for singing-confident Pew Lutherans Et Al. does not readily swim the Tiber except for Christmas standards and the like.

Consult the voices of your very weakest mezzo and baritone* choristers in terms of what keys/pitches and melodies are most plausible to for Pew Catholics to sing in early through mid-morning vs midday through evening AND early in the Mass vs later in the Mass (Pew Catholics get NO warmups).

* Why them? Because they represent over a majority of typical voice distribution, while true soprano, contralto, tenor, and bass voices are significantly less typical in the pews even if they are more typical among music directors and organists (who, if they have perfect pitch, must be able to transpose according the singing needs of the pew singers - I vividly remember a TA in my second year of music theory (after a year in high school) deliberately transposing his sight-singing exercises by a tritone after taking first attendance of those in the classic who identified as having perfect pitch - Mr Giffen, did you ever have reason to encounter a different Chuck in the Music Department at Mr Jefferson's University? Being a hornist drilled to do all manner of transpositions on a dime, including the dreaded tritone - hey, Brahms' Second!, scored in B for horn but played on an F instrument - I could not help but love that).