I don’t know if it’s acceptable to the Thai government but I just flew to Indonesia with Emirates and was given travel insurance including covid cover free ( inclusive) with my ticket. Valid for duration of trip. Worth checking out.
, it a rule still enforceable, just what an immigration officer needs if he decides, whether you have a visa or not. 20,000 Thai bht or it’s equivalent in any currency is no big deal to carry. No ATM air side prior to immigration...