Just changed my O based on marriage to retirement 800,000 in bank for 3 months fill in a form and go to immigration. Easy.

Not required, for O

No.

As Robert says. Try around all branches have different ideas. I had no trouble with Kasikornbank but had problems with others.

Just put ' unable to fly due to Covid 19 restriction' that's what I put and was accepted.

More to come I fear.

Just did mine 6 months late. Or if you wait for 12months you re test. You also have to do all the eye tests and go sit through a 1 hour video that you have to book in advance costs 200bt you need that for the application to renew and I had to get a declaration from Immigration to say I lived where I live. All got more complicated than last time.

I have Australia passport got stuck in UK not a resident just filled in the information I could and sent it. In Bangkok now OK. Multi 'O' visa. No problems.

Russia

Your local Thai embassy site.