Please help, advise, or look into bugginess deacribed in my personal notes. I would go back to QkSMS or look at alternatives, yet I understand (still?) the customized AOSP Messaging App is the one that works well across many profiles, where I have some that are restricted from SMS for kids to play games on.

Platform: Pixel 7 Pro

Messaging App

Does not respect default setting of "Pop-Up" messages showing on screen, which can be controlled by...
Messaging, at some point, came up with a weird anti-feature within itself called "Conversations". The first issue can be fixed on a person-by-person basis, where "Pop-Up" is always the default for new messages, including to known outgoing contacts AND incoming messages from known and unknown numbers (#1 being disrespected).
Weird lists get made and become corrupted in the context-menu (long click) of the Messaging App. The name of the App itself disappears at the top part of that context-menu, but only once it is broken (broken: when something is marked as a Conversation or Not a Conversation). These other items that accrue can contain duplicate entries (Contacts?); they don't track properly with Contact updates; there's even a special "bucket" you can place some of these in to specify that it is "Not a conversation". I don't understand.

In short, none of the feature makes any sense. Fixing would be great, unless it breaks something else, which may take some time to tell. Try fixes below for now. File a bugreport once lab is set up and computing capacity within the lab is able to build AOSP. Without income, this will not occur.

FIX: Having ZERO clue what this might "break", RcsService (a hidden / internal) App installed on the phone has a "Special Permission" to "Modify System Settings" out-of-the-box. CHANGE this permission to Disabled for that App.

UPDATE: This first FIX method worked for outgoing messages, so they won't create Conversations and break the App.

UPDATE: It broke on the first received text message, however ("Pop-Up" notification showing and all explained above).

Other FIX: By clearing the App's cache, stopping it, AND clearing the App's storage, at least the whole name mismatches and duplicates and nonsense are taken care of. Everything is removed and is how it should always remain. However, now, all new messages (sent or received) will go back to back to the "Pop-Up" bubbles, again contradicting the master notification defaults set by the user.

NEXT TRY / FIX MAYBE: Disable the whole RcsService app, and repeat "Other FIX". It's an internal / hidden App. Hence the verbosity noted in this paper. Testing...

NOPE: Though the DISABLED RcsService App (which appears to be the one causing all the stupid fuck) is disabled, it continues to become activated somehow. Something else, probably more internal, activates it, while the status of the App remains disabled, which the options to Clear Cache/Force Stop/Enable.

I just dong understand the reasoning for its existence. It's obvious how insecure SMS / MMS is, but this weird notion / nomenclature simply does not "click" in my logician's mind. And, bugs are clearly and easily reproduced out of the box, with only one profile (Owner).