Whenever the phone heats up the phone turns/switches 5G into 4G.. this is how Things work.. it's because overheating can Damage your phone PERMANENTLY!
You can do two things to prevent such Switching - 1. Report the Heating issue to Samsung, they may fix Heating issue in future updates.
2. (Till they fix Heating issue) Don't let the phone heat so much.. by Reducing Screen brightness (use below 20%), Avoid using phone in Direct sunlight and when Ambient temperature is HIGH & avoid heavy task .. avoid using Thick Back cover etc.
- I know this sounds Bad.. but.. This Switching of 5G network wouldn't stop happening until they fix the heating issue (my experience).
What provider are you using?. If you are using jio SIM and mostly using voice calls and during travel, then change the network mode to 4G only or LTE only mode under the phone settings.
