As stated before, Aetna covers covid expenses up to your plan's limit, then 80% of any costs running over that limit. No pre-pay. Aetna acquired BUPA Thailand awhile back.
All that aside, with so many much better, happier options in the West, why come here now unless returning expat to reunite with family? It's not the country you remember, not a fun place anymore, far from it. Nothings really open-open. Rules, zones, over pricing, checking this and that, unpopular dictator ruler. Unreliable testing, no one knows the true covid numbers. Rip offs from day one until you're finally, hopefuly able to get out.