Before selling it and passing on the issues to a new owner maybe try Safe Mode @Manihasani
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/
A Samsung Experience Store or Samsung Service Centre can take a look at your phone.
I wish you all the best with this.
Current Phone > Samsung Z Fold³ 5G.