Can I withdraw funds from a Thai bank account back to the US on a retirement or marriage visa?

I believe you can do a wire transfer to the U.S. using the SWIFT code the same way you can wire money to Thailand.

Yes, as long as you have mobile banking you can transfer the fund to your account anywhere and you should try to do the transfer while you still in Thailand. If your mobile banking error or can't go through then go to your bank and ask them to check. I use Bangkok bank for mobile banking and always good.

Hi. Well with me (Dutch/Netherlands) it worked several ways. I have the Bangkok bank app and Kasikorn bank app installed and with both there is an option 'international transfer'. I tested this with a small amount to my Dutch bank account and the transfer worked. Also took my Kasikorn bank debit card with me, and also that worked in a Dutch ATM. To 'transfer back to home country', there are also apps available to reduce costs, but I never registered nor used them. With the famous "WISE app." you can only transfer back if you have a Thai Mastercard. Ofcourse you can use the bank apps in y'r home country, it's 'just internet'. But the apps have to be installed in Thailand I guess. Also, Visa extension related, you have to watch for (min.) requirements of funds for the relevant extensions, to keep the year extension alive if you want to come back when you bought a re-entry permit before you left.