I am pretty sure getting a tourist visa in 2020-2022 was mandatory to have the jab. In fact I do recall being forced to book a room into a special hotel for testing of covid before being allowed to roam Thailand.
System was like being in the movie Outbreak. I arrived at Suvranabumi. Passengers were guided to special area where we were given seats all spaced apart. Someone checked out temperature, papers, and then we were put in a private car and driven to the special hotel. There we were swabbed for covid and put into our private room awaiting results. All the staff were masked and gloved up. Felt like I was unclean and they would kill me if I sneezed. Morning came and results were OK we were allowed to go to our hotel and do Thailand stuff.
So yeah I'm pretty sure vaccines were mandatory. Perhaps if you LIVE there and have as resident visa it was different.