I was told that a letter would be accepted by immigration. However that was not the case. I had a 1 day overstay and 500b fine. The only way is to get someone go on your behalf
I was in the same boat. Unfortunately I had to pay the and get the stamp in the passport even though I had a letter from the hospital. They said I should have come to immigration before I got covid as if I knew I was going to get it. They did say that a friend or hospital staff could have gone to immigration on my behalf though. This might be an option. This was in Bangkok
I didn't need my tm30 for my 30 day or 60 day extension. I was seen by the same man both times at mtt. But a friend of mine was seen by a lady and was asked for his. So basically it seems its luck of the draw