I've got an Oppo A5 2020 and it came with its own Messages app which I promptly replaced with the Google Messages app. Unfortunately I can't remove the Oppo app and it has a permanent "1" indicator on it to show that there's an unread message. Nothing I do can remove the "1" indicator, even after I removed all permissions for this app. My last phone had the ability to disable stock apps but this new phone has the disable option greyed out; seems like Oppo don't like you disabling their stock apps.
Intersting - are there any OS updates for it? Yeah I remember the 'older' Oppo's wouldnt allow you to change the 'default' apps and the newly released phones all used 'stock' android apps (looking at A52, A72, X2). I think the A5 was the last gen of Oppo's.
Xiaomi also ship their own SMS app with more recent models (e.g. Note 7). It's not great though, I was really happy when I found out I could get the stock SMS app from the Play Store instead! One feature I must have is the ability to archive SMS messages which the stock app has. I don't understand the point in their (e.g. Samsung, Xiaomi, etc) reinventions of the wheel. Is there any practional or functional features these stock apps do that the stock SMS app don't...?
For sure - was mainly looking at the carrier devices otherwise where do you draw the line! I personally have a Mi9SE and have wifey on a Redmi Note 7 (with pixel exp ROM).