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 .