I am planning to go to KK in a week or so and just looking at my options. I do not have a car so its a choice between bus, train or plane.
Travelling by air does not seem a problem from accounts on-line except for the Mor-Chana app requirements.
Looking at bus companies, some state only Thai nationals (Budsarakam Tour) can travel. Also one on-line report from last week states Nakonchaiair only allows Thais.
Trains seem to be running OK but I cant find if foreigners are now allowed to travel.
Hopefully somebody can confirm which bus or train optio