, you are correct, there is not such thing as retirement Visa, it is farang who gave this name. Also a “non immigration” as called above is also not existing, it’s non immigrant, from any kind of type Visa.
Asking for OA in your country only require proof of 800.000 in any bank. But the one year extension requires that amount in a Thai bank, or proof of income of 65.000 a month.
That’s just in case they should ask you can prove the money is legally and not laundry money! But don’t worry they check only one out of.........so many..