Help upgrading Android 9 to 13 or stable version?

[i7vSa7vi7y]

My young son uses my 6t just for gaming. Right now it has TWRP 3.2.3-2 rooted with magisk and is running Android 9 Oxygen ROM Tmobile phone but its unlocked.
I'm not new to flashing but just wanted to get pointed in the right direction. I have been away from the scene for years. How do I go about flashing from Oxygen 9 to a stable Official or custom ROM on Android 13 or any stable android version for this phone?

 

[Zarbok786]

Most roms require you to update to oos 11 first before flashing the custom ROMs. For android 13 I recommend crdroid which is the one I use, instructions will be on their XDA post which is on the website. I don't have the T-Mobile variant and lots of people seem to complain about it, good luck