I did mine 60 days before... really depends what office

If he gets caught by Police on overstay before he departs he will be arrested, detained, fined and possibly blacklisted, it has happened.

Jomtien only requires the lease and ID's, not the house book. But never hurts to have. They also accept the form completed by yourself, not the owner. Fairly easy process there.

Repeating old news...

Did you or the owner of where you are staying in Chanthaburi lodge TM30 reporting your stay in Chanthaburi within 24 hours of arriving, as required by law?

First you face a fine for failing to do so, but also some provinces are locking down and no foreigners (who haven't registered as living in the province) are required to leave - no exception.

Correct, normal first 30 day extension does not require Embassy letter.

And the day you arrived back is counted as day 1

TM30 requirements still exist, otherwise fine

Why can't you fly back to Australia?, it's not closed to Australian citizens or permanent residents, and immediate family members!

It's highly unlikely the US Government would ever close its borders to US citizens, rather they are more likely to invoke mandatory supervised isolation for a period of time on arrival.