As a few people have suggested, it does seem T-Mobile has changed/fixed something in the server side in the last week so it's slightly fewer steps and more stable.
A few weeks ago I got RCS working by doing the uninstall and reinstall with the older 242499063 version method. The first time I did it I had to clear the app data, but that hasn't been necessary since. It always did the usual Connected: true Etouffe: false until the update, then Connection error with code 3000 or 3200 until a reboot or two (or wait a bit then reboot once). When messaging 1-on-1, chats would stay MMS until you sent the first message, regardless of how many you received, and then switch to RCS. And groups that had upgraded to RCS were intermittent whether or not they'd deliver the RCS messages you missed from the last month after you got re-setup.
This week though, it's now no longer been necessary to do the final reboot(s) after the update. It reports Connected:true and Etouffe: true immediately after the app upgrade. 1-on-1 chats also upgrade immediately after incoming messages as well now too, and missed group RCS messages from the last month are consistently delivered.
I never tried it before, but this week I had a case with non bars and only WiFi. I'd done the no-reboot methodon the last re-install, and RCS said it couldn't connect when I had no bars. On a guess, I rebooted without doing anything else (the first after the Messages app upgraded to the latest) and RCS started working fine over WiFi too.
The re-install is annoying, but using Aurora Store exclusively from my main profile is pretty fast now. Not wiping the message database means I don't have to wait 30-45 minutes for it to repopulate, and luckily Messages has almost no settings that can be changed (though I do have to toggle almost all of them off, and the new versions added a new Gemini option to also toggle off after upgrade). My biggest annoyance with it is needing to re-setup message notification ringtones and re-pin conversations.
Caveat: Not clearing the database may cause crashes when there were large pictures sent in a conversation. I sent a picture in one conversation via RCS with the "send pictures faster" (via Google Photos) disabled, and that conversation would crash after a second every time I opened it after the next reinstall cycle. I had to use a different text message app, set to the default temporarily, to delete the photo from the conversation to fix it. It might have been solved with a full database re-import by Messages once on the latest version, but I'm not willing to do that every re-install cycle.