First, every large church that we visited without exception had a sound system that was unobtrusive, consisting of very thin columns of speakers about 4" wide and not very tall placed vertically on columns throughout the church.
As such these carry only mid to frequencies - which travel short distances and die quickly. Unlike the US audio designers who insist on a large array of speaker cabinets with the ability to carry full sound for singing and playing of instruments including the bass guitar (another nod to the Protestantization of the Catholic church in the US) these very affordable speakers work well to make speech and singing of the priest clear and intelligible to the congregation - as well as cantors.
Many of these churches had small video screens at the large organ with a small speakers to be able to follow the Mass.
Lacking the full range of US systems with emphasis on bass, these speakers eliminate that massive rumble that makes song and speech unintelligible, instead providing clarity and quick silence.
At St. Sulpice and Notre Dame the organists both improvised before Mass and ended up with an introduction to a hymn, words printed in bulletin, which the congregation sang.
At St. Sulpice there was no choir, merely a cantor at the altar who led the singing.
The ordinary of the Mass was in French, with a setting that I believe is one of the usual newer ones.
During the offertory the organist performed an organ piece and the priest waited for its conclusion.
During the communion the organist also performed a piece and the priest waited for its conclusion. At that time a congregational hymn was sung as a post communion song, the second and only other hymn. However, the last verse was followed with an improvisation on the hymn that was chromatic, dramatic and ended with full organ. The priest gave the final blessing and the organist began an organ recital.
Speaking with the cantor, I asked if they sing to hymns instead of the four common in America, he answered, "When the choir is not here we like to give the organ it's voice."
Notre Dame was a bit different, it was the mass of the cardinal, I believe, (the organ loft is a long way from the altar...) the music was different from Sulpice in that: The offertory and communion were sung by a quartet - wonderful polyphony. The Gloria and Credo were sung in Gregorian Chant in Latin by the congregation. The remaining ordinary was sung in French to more recent music, like Sulpice.
Both churches chose music for the congregation that was well-known and as a result they sang.
This was a research trip for a project we are involved in and was a wonderful experience as part of an organ tour that occurs every 2 years. Participants are given options, including playing many of the organs, being in masterclasses and private lessons.
All churches visited - about 17 in Paris - surprisingly, had a simple printed sheet at the door with the words of the hymns and readings for the Mass that day.
If you want people to participate, they need something in their hands to follow.
As a Parisian, I would just add some complements: here in Paris, all parishes provide a hymns sheet, with the hymns of the day or liturgical period. Most parishes have the responsorial psalm on it ; some also add the readings, but it is not as common.
Here (in the suburbs, so not the same diocese) we have the hymns, the response of the psalm, and there is a debate about whether or not to add full text of the responsorial psalm. No readings, except on special occasions.
In my former parish (inside Paris), we had the hymns and the responsorial psalm (full text), but not the readings. There was a "Gregorian Mass" with a schola singing from the Graduale Romanum, and they provided a special sheet with with text and music for the chants, so you could join if you felt up to, especially for the ordinaries.
I understand you were surprised by the absence of any hymnal. Actually what happens here in France is we got an ugly repertory in the 70-80's, with music from not wonderful to quite ugly, and lyrics from not wonderful to ridiculous (the Holy Spirit opens the windows and makes eolian electricity, and I hardly exaggerate) or cryptomarxist (Liberation theology says hello).
Then grew up some "New Communities", very focused on spiritual things : the Communauté de l'Emmanuel is the most well-known. They created new hymns, with lyrics directly from the Bible (Psalms, Isaiah, the Gospel...), and music not wonderful (sometimes too bouncy). Still, on the lyrics part, there is a wonderful progression. This music slowly is replacing the former one. The former one had hymnals, but these are now outdated nearly everywhere ; the new music doesn't really have yet any hymnals, since there are still a lot of new hymns written each year. Most of the hymns in Paris are now issued from this repertory, or from the best of the 70-80's repertory ; that is less true in the suburbs and the countryside, where, alas, we sometimes still have cryptomarxist stuff (promise to self : I will get this awful "Wind of Tempests, Open our Windows" out of my parish, one day.)
Then... it's not finished. Some people are getting at work to renew the music and not only the lyrics, with inspiration from traditional polyphony.
Well, everything is in such movement that no parish would risk to pay for a hymnal that would be outdated three years ahead...
To participate in the discussions on Catholic church music, sign in or register as a forum member, The forum is a project of the Church Music Association of America.