There are some good generic troubleshooting options you can try.
First ensure your phone's software and your apps in the Playstore and Galaxy Store are up to date.
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. https://www.samsung.com/uk/support/mobile-devices/how-to-start-my-galaxy-device-in-safe-mode/
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. https://www.samsung.com/uk/support/mobile-devices/how-do-i-clear-the-cache-on-my-device/
A Samsung Experience Store or Samsung Service Centre can take a look at your phone too.
If nothing helps from this thread i.e Safe Mode or clearing the phone's system cache files, or from a forum search or a Google Search then I'd suggest going to a Samsung Experience Store or Samsung Service Centre.
Thanks for the help. I've cleared the cache partition and will see if this clears the problem. If not, then I'll try a factory reset and reload the apps although this will take a lot of time (they're all from the app store and there were no problems when they were on my S10). Read somewhere that it may have something to do with setting up the phone using smartswitch. Disappointing really as this seems to be a common problem and some people have had their phones replaced. Not what you'd expect from a premium phone.
Have now done a factory reset and reloaded my apps direct from the app store. No random reboots for 3 or 4 days, until today. Looks like it's a visit to a repair store.
Phone taken in to a Samsung Service Centre. Couldn't find anything wrong. Flashed the software and then reinstalled it. Only time will tell. If this doesn't work then it will have to be a warranty claim for a new phone
