I noticed that mobile hotspot in 2.4GHz mode doesn’t work anymore since the Android 11 update (My phone is a SM-A405FN TIM). When in the settings I can click on the button to activate it, the spinning wheel appears and then I shuts itself off again. Sometimes it works after restarting the phone and or repairing the apps in recovery mode (pover and volume up to start the phone). I have seen many users have had the same problem and I hope you will be able to solve the problem in a future update. Please write me back if you read the conversation and have found a long-term solution.
So far the only reliable solution is to switch to 5GHz mode.This of course has its own drawbacks,but Samsung is beginning to rollout an update which should adress this issue.
Hopefully it comes soon.