I share with you my own harmonization of the Royal Mass in the first tone by Henri Du Mont. There is a different Polish harmonization from the one I am presenting here.

I am not a musician, but just a good amateur. This harmonization I have done thinking of other amateurs like me.

Here are the audios for those who want to know this solemn composition.

Kyrie: https://www.youtube.com/watch?v=csSTIlYhc_o
Gloria: https://www.youtube.com/watch?v=06xGm2iCmCo&t=108s
Credo: https://www.youtube.com/watch?v=fFxaaXqPvWU
Sanctus, Agnus, Ite missa: https://www.youtube.com/watch?v=bKxYo8EjjPs

These other posts talk about that mass:

https://forum.musicasacra.com/forum/discussion/6567/henri-du-mont-messe-royale-where-to-find-music/p1

https://forum.musicasacra.com/forum/discussion/12884/inspiration-for-the-kyrie-of-dumonts-messe-royale/p1