I assume your apps are updated ?
If your using any apps via an apk then consider deleting to see if things improve.
Remove your sd card if your using one as a sd card that's glitching can cause issues.
If your internal storage is getting full then consider deleting unused items or rarely used items.
Go into your device care or similar named section in the phone and use the tools there to clean up unused files and your Ram too.
So here are some generic troubleshooting tips that may help.
Clear your phone's System Cache Files by turning your phone Off and then from a set series of button presses go into the phone's System Files and clear the cache. No information is lost this way. You may need to insert your headphones or hook upto a computer with your data cable to get to this menu on the phone.
Put the phone in Safe Mode which disables your downloaded app's but let's your stock app's keep working. If the issues stop then this highlights a downloaded app as the possible issue. Come out of Safe Mode and start deleting your most recent downloaded app's one at a time until it stops.
Back up and remove any relevant sd card and factory reset.
Current Phone ~
Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+
Samsung One Ui 3.1/ Android 11.
Thank you for your reply, I did as suggested and by Friday the phone completely died. It won't turn on or charge. Not sure what can be done. Tried the power + volume key and still no power. Any suggestions please