Visa on arrival was a thing in Thailand pre Covid. It was only for a reasonably short list of countries and only good for 14 days making it moot given quarantine. Even visa exempt which is maybe what you were actually asking about is not available in these times.
I can only say that the only Covid cases in Thailand are from people entering the country is an absolute fever dream. Those are the only ones being tested. I am not saying Covid has been a disaster in Thailand in any way but the official stats are sooo suspect. How many people die in the villages without testing or a reason of death recorded?
I am afraid you are getting about 15 steps ahead of me. I have never personally gotten an extension as I have used multi entry tourist visas. Every permit to stay I have ever gotten on initial entry or subsequent entries have been in the form of a red stamp directly in the passport. In your case I really cannot say what this document in your passport is. In your photo I note a reference to the Kingdom of Cambodia? Perhaps that just sneaked into the photo from another page on your passport? In normal times a permit to stay based on a single entry visa can only be extended one time. The visa amnesty made a mess of all that. I am not sure what is planned regarding amnesty and I am not sure the Thai officials do either. I think it might be time for you to go t Thai immigration to get sorted out.
I would say you are mostly correct. Things get a little more confusing with a multi entry visa but with a single entry visa, your visa is done the minute you walk up to immigration. What you get is a permit to stay stamp in your passport which can vary depending on the type of visa you had. The permit to stay can be extended to new permit to stay at immigration. It is obvious you understand the concepts, I am just trying to help a bit with terminology.
I would not hold my breath e on the STV. My understanding is that in Covid times ED visas are only being granted to University students. I assume, but do not know for sure that it would also apply to someone applying to convert in country. My guess is that there have been way too many people abusing the ED and volunteer visas as an excuse to stay in the country.
I am Canadian what province is the scammer living in? I ask because some provinces have their own provincial police force while others depend on the federal police. It can even come down to city by city. I live in a large city with its own police force but some suburbs depend on the national police as we do not have a provincial one in my province.
I know there are restrictions on leaving Aus but do not know the details. That said I believe the STV scheme has essentiially been dead on arrival. The STV is not available in my country so finding info is more challenging but I think I read somewhere that financial requirements have been dropped to try to bring it back to life.