Masks and vaccines are NOT designed to prevent the spread of infections. They are there to lessen the effects of covid/infections and both are proven to work very effectively.
The OA is also often referred to as a retirement visa but the commonly used 'retirement visa' is the Non Imm O, it's issued for many reasons, ie being over 50(retirement), marriage, dependancy and volunteering. The irony is there's NO official retirement visa and you dont need to be retired to get the Non Imm O or the OA.
Buy the Non Imm O visa based on being 50 or over, commonly known as a 'retirement visa' from the RTE London via the evisa system. This gives you 90 days on entry to Thailand enough time to open a bank account and season your 800k bt for 2 months. You then apply for yearly extentions of stay based on 'retirement'.