I got married Nov-21. I got the Freedom to Marry paper from Embassy (🇬🇧) in Bangkok and used Siam Legal in Bangkok to translate to Thai and they took it to MFA to get certified/legalised. At the time the MFA were not accepting walk-in document legalisation due to COVID restrictions - I piggy-backed on an existing appointment Siam Legal had booked. Things may have changed now but it’s worthwhile double checking with the MFA before making the trip to Bangkok. If you use a 3rd party to go to the MFA you will need to give them Power of Attorney so they can legally represent you and complete the process. The complete process for me from 🇬🇧 Embassy to having the legalised document in my hands ready to go to Amphur was 5 working days.
As others have said, it really depends on the individual branch.
I opened an account with SCB in Hua Hin about 10yrs ago when on Tourist Visa. Very straight forward, just needed to show certificate of residence from immigration. I opened a 2nd account with SCB earlier this year in Sisaket on OA Visa. Again very straightforward with certificate of residence from immigration.
I just arrived in BKK on KLM. A bit of confusion in Schiphol getting all the Covid related paperwork checked but apart from that the flight was fine. Staff very friendly, good service, food OK (certainly had better) and hardly any passengers so plenty of room to relax.