there was no plane to the airport for Pattaya which is quite far south, from Chiang Rai when I visited in May of '22, starting the day they ended the 1 day quarantine. I went up through Chiang Mai to Chiang Rai, over 10 days. I had to take a bus back down to Bangkok and then a mini-bus to Pattaya. I'd probably find a limo from BKK to Pattaya if I were doing that again.
I like Monmondo, as it can handle "broken" flight segments, where you have short stays at intermediary stops. It's almost faster to get to Pattaya by way of Bangkok.