Hi @fake72773,
Try starting the phone in [https://safemodewiki.com/enable-safe-mode-on-and-off-in-samsung-galaxy-m31s/|safe mode] and check if it starts OK.
If it does than a ''downloaded'' ''app'' may be the cause of the problem. The trick is to find out which one.
You will need to uninstall each ''downloaded app'' one by one, and then start the phone in "normal" mode between each uninstall to see if it starts OK.
When it does the last ''downloaded app'' that was uninstalled was the problem. A ''downloaded app'' is one that you downloaded and installed and didn't come pre-installed with the phone.