What is the current duration of a visa on arrival in Thailand, and can it be extended?

I think you've got your terminology mixed up 😕

A visa on arrival is SOLD to people from 17 countries when they show up here for 2000baht and it's good for 30 days

I think what you're asking is about the visa exempt entry <- Free entry stamp, it's not a visa on arrival, it's not a visa at all, it's just a free entry stamp. People from 52 countries get a visa exempt entry when they show up here without having bought a visa from the thai consulate before they arrive

Right now (and until Mar 31) the visa exempt entry program lets people in for 45 days and you can extend that one time for 30 more days at the immigration office that serves the area where you stay.