My S21 isn't even a year old and it keeps trying to "boot itself up" when I turn it from "off" to "on". It's like something is stopping it from completely booting up, so it shuts itself down, then it tries to boot itself up again and can't---so it shuts itself down, then it tries to boot itself up again and...... This goes on and on and on until the battery is dead, about a day later. It's kind of like a dog chasing its own tail.
Previous to his, I have not added any new apps and couple days ago I replaced the battery, not long before this started (couple of weeks) I did check for updates on my firmware and apps and everything was up to date. I googled the problem and it seems like some people out there have the same problem the first post of the problem in late Oct.'21, then a few more in November, me and others in December and we're all scratching our heads and then I found this forum. Is there a way, like in Windows 10, where you can take an S21 Android and go into a "Safe Mode" to see what's going on in there, and how do you interrupt the "boot-up sequence" in order to do that? Androids have some kind of safe-mode thing, don't they---I hope!? HELP!
- Constant rebooting
Now, off to the Maintenance (Recovery) screen:
Press and HOLD the Volume Up key, and while holding, press and HOLD the Side key.
When the Samsung splash screen appears, release both keys. Within a few seconds, you'll see the Maintenance screen, with a number of menu options.
Use the Volume Down key to highlight Wipe Cache Partition. Press Side key, select "Yes".
Now, Use Volume key to highlight "Repair Apps" (should be last menu option). Use Side key to select it.
The phone will automagically restart.
See if that helps