From the US Embassy website:

"10) What type of COVID test is needed?

Upon checking in at the departure airport, the approved applicant is required to present a medical certificate with a laboratory result using RT-PCR test indicating that COVID -19 is not detected. Such COVID-19 test result must be issued no more than 72 hours before departure."

Your best bet for each country is their Foreign Ministry website.

When you add your flights your final COE will reflect date of arrival.

@Gary ******

Yes I've done it. Not a single stamp in it, absolutely brand new.

Definitely now.

Yes. The current outbreak spread through bars and clubs starting in Bkk, so a ban is in effect until further notice. You can still buy in supermarkets, , etc.

Stated by whom?