I live here, I have had no problems, but a couple years ago, numerous people posted here that they were living here on back to back tourist visas and visa exempt, and that’s the excuse they used to deny them entry
If they required the 20,000 baht, you have to have cash in baht or a major currency. Credit cards bank books and showing it online would not do. In 2019, before Covid, if you had too many tourist visas or visa free entries, they would not actually ask to see your money, but they would write on the passport refused entry, does not have sufficient funds. Because, there was no rule against having many such entries, but among themselves they decided not to let people in who were living here on tourist visas. Hasn’t mattered of course since Covid.
Krungsri Brought out several forms just for Americans, and we Americans have to make an online report if we have more than US$10,000, and a higher level report I think if you have over US$50,000.
They have the strange paranoia about opening accounts for foreigners who do not have work permits, on tourist visas or retirement visas, etc. You really have to go from branch to branch and bank to bank. I got mine at Krungsri. Also Bangkok bank occasionally tells people that they cannot have mobile, Internet access, nor ATM cards. I think it goes back to an old rule that pensioners needed to prove they were alive by coming to the bank each month. Don’t except that, try another branch.
If you have a thai Sim, and you have it with you, try calling your phone company such as True or AIS. Ask them if they can give you international service. I did it when I was in Thailand with True, they were glad to give me international service and 10,000 baht credit in case I need to use it extensively. I never had to use it, but that way when I traveled outside of Thailand, I would be able to use my Thai -number as normal even at a high cost per message and receive the OTP.