

Aside from finding a tutorial for that, of which there are surely hundreds or thousands online, I’d also suggest checking ProtonDB on the off-chance that the game actually just doesn’t run on SteamDeck: https://www.protondb.com/app/2050650?device=steamDeck
I assume you meant that one, looks good and commenters there also give some info on what they did to start it.
Generally speaking sure but the Gmail to Tuta one is not really helpful. Tuta is a completely different provider, I am not saying you shouldn’t switch but this isn’t switching your app but instead your whole e-mail presence.
Maybe a better choice would be Thunderbird as mail app instead of Gmail if you don’t want to switch addresses.