I think you might be talking about the new digital arrival card, as of May 1st, 3 days prior to flight you need to apply online for the TDAC (Thailand digital arrival card), everyone has to apply for it when entering Thailand
You need 6 months left on your passport from your return date as we just discovered with my son's booking, he had exactly 6 months from departure date but when he went to do his online check in, it wouldn't allow him to do it, lucky we were able to contact Air Asia and say why did they allow him to book the tickets in the first place if it's meant to be from the return flight date, they then did his check in from there
When deciding to move to Thailand, you do your research on rules and regulations and always check as policies change, should always keep yourself updated on requirements