Does a retirement visa fall under a specific category and can it be issued while staying outside Thailand?

Up until very recently the non OA visa was the only option of entering Thailand as the Non O’s were not allowed. However a few embassies has now stated that valid visa holders could apply. They won’t sell you a new one, but if you have a valid one you can apply for a certificate of entry.

A non immigrant OA visa is a “retirement visa”. There is also the non immigrant O visa based on being retired, which can also be called a “retirement visa”. You can get to OA visa from you local Thai embassy/consulate in the country of your passport. In “normal” times you could also get the Non O, but many places won’t sell you that currently.