They are butt hurt. This is nothing more than crying over individuals expressing a belief that there is something more important than themself, greater than themself.
It actually is possible to reject someone's belief while allowing them to pray in a public space. If it's not in a dedicated reigious building, they are not harming anyone by saying words.
That's the only reason I won't use Proton, because the app and the network is not clean. The best security encryption is made from public protocols, so app and servers should be open source.