I dealt with this on a flight October 30th arriving November 1. This was when the quarantine went from 7 days to 1 day. Qatar airways almost didn’t let me board in SF because ticketing staff were not aware of the change. They made me wait about an hour and ultimately a boarding pass was issued.
The opposite happened when I tried to go to Malaysia through VTL. Denied boarding despite VTL being opened for 8 days.
Not every ticketing agent will put in the work to solve the problem and get approval, do the Thai pass—it’s easy and free (aside from insurance)
If you do make it through the red tape, no quarantine unless you test positive upon arrival. From my understanding it’s a free PCR at the airport somewhere between gate and baggage claim