Please help to fix and back up Android 12

My Pixel 4 with android 12 is experiencing an infinite rebooting problem for unknown reasons. I suspect something is wrong with the google app, which is not able to be updated without errors. I tried to uninstall some apps to create space to update all the apps but the phone is forced to be rebooted every few minutes after I unlock the screen. And empty space got mysteriously used up after every reboot. I can't find a working solution and I am now trying to back up everything on the phone, except I don't know how to. Pixel 4 was previously rooted but it is not rooted after updating to Android 12. The bootloader is remained unlocked. I found some answers but they are dated and I am not sure if they still work. I need solutions to back up all apps with data. For example, Messages, WhatsApp, WeChat, Game data. Ideally, I need ways to back up data in recovery mode because the phone will reboot every few minutes after the screen is unlocked. Please give me exact instructions on how to perform the adb instructions. I have not performed these instructions for a very long time and I forgot everything. It is very frustrating to find out that the official google backup solution is to use google one as the backup solution. I highly doubt if it actually backs up everything including game data and app data. And it seems like it is useless in this case because the backup occurs after unlocking the screen, and not at the recovery mode level. Thank you very much for your help.