Have you tried to troubleshoot it by wiping the cache partition?
I personally encountered this problem before and fixed it by simply deleting the system cache. It’s because there are times when the cache gets corrupted or becomes obsolete, especially after a firmware update. The system cache needs to be deleted from time to time so that it will be replaced with a new one. You can do just that and possibly fix this problem by wiping the cache partition. Here’s how you do that:
Turn off the device. Press and hold the Volume Up key and the Bixby key, then press and hold the Power key.When the Galaxy A20 logo shows, release all three keys. Your Galaxy A20 will continue to boot up into the Recovery Mode. Once you see a black screen with blue and yellow texts, proceed to the next step. Press the Volume down key several times to highlight wipe cache partition. Press Power key to select. Press the Volume down key to highlight yes, them and press the Power key to select. When the wipe cache partition is complete, Reboot system now is highlighted. Press the Power key to restart the device.
Once your phone has successfully rebooted, try using it like you always do and see if it still keeps restarting.