Every time you leave the Country and re enter to have to inform immigration with in 24 hours of your place of residence. Even if you are returning to a Condo you personally own.
I usually just use the apps to find the cheapest flights and then go to the airline to book. I booked a flight in July for Canada. Lufthansa was the cheapest and I got the same price booking with them directly. My Itinerary changed due to canceled flights but left me with very long layover. I just called the airline and they booked me with another Carrier. Was an easy fix because I was dealing right with the airline and not a travel app.
Thailand has been one of the most generous Countries in the world for enabling Foreigners to stay in Country during Covid. Many people have been here over a year just on Covid Extensions.
Your best bet is probably check the ED Visa . I know it is expensive, but flying back to Austria then applying for Thai Pass which means Booking SHA Hotels paying for Covid test before you get on plane and 2 Covid tests 5 days apart once you get back to Thailand then on top of that cost of STV and Covid Insurance it will also be expensive. You may be able to get a 6 month Ed Visa for a little less than a 1year.
I think if you want to retain that Visa you have to leave and return before the Expiry Date on the Visa which is June 10/ 22. Once you go past that date the O/A Visa is void .
As a Canadian I still file taxes every year on Pension income earned in Canada. I just give them a copy of my tax returns taken from Government Website with my SIN number. (gov. Issued ID number) Then with my permission they go to Government Website online verify and issue the letter. Very simple only takes them a few minutes. I don’t understand why the U.S. and the other countries can’t do the same.