I used to use the SNCF app + Île-de-France Mobilités on my Fairphone 3 running Murena /e/ OS, but that died and my Pixel 6 also running the same version of /e/ OS will allow me to buy, but refuses to actually store the tickets, which was fun when I was connecting a train via the Metro.
None of this would be a problem if you could actually mail order a Navigo pass from anywhere outside Île-de-France, but no, that is not a thing RATP does.
(Apologies for chiming in with a rant, I've had this brewing since Feburary.)