score:4
As of August 2022:
In Thailand, COVID is effectively "over". If you are vaccinated, there are no special entry procedures, and once in the country there are no COVID-related restrictions, QR check-ins, etc. Masks are no longer mandatory anywhere, although they're still recommended and quite common especially in Bangkok, but much less so in the beach resorts. I would imagine Chiang Mai would be somewhere in between.
Korea remains more strict: you are required to take a professionally administered pre-departure ART/PCR, and another one on arrival. I haven't been to the country since they reopened, so I can't speak from personal experience, but I gather masks remain mandatory in most indoor settings. Most businesses are open normally and QR check-ins are only required for high-risk environments like nightclubs.
So, if minimizing COVID hassle is your sole criterion, Thailand is the clear winner here.