The rules have not been so clear recently because they have been changing a lot as the scale of covid has changed – which is understandable.
For now, if you are vaccinated, you can travel to anywhere in Thailand.
If you have a PCR test, you can travel to fewer places.
No test, you are effectively exiled to Bangkok.
The situation on the ground is changing all the time as the covid numbers are now decreasing, so please keep your eyes and ears active.