Can I transition from a COVID extension to an Education visa in Thailand?

I would say talk to your school, see what they recommend you do. I mean you have a 60 day tourist visa entry, you're going to extend that by 30 more days <- that's 90 total, certainly you should be able to enroll in a school and have them get the documents from the Ministry of Education so you can go to the immigration office and apply for the 90 day Non-ED visa without needing to take a 60 day covid extension.

IF your goal is a long term stay here, get after getting the correct visa so you can stay without jumping onto the "covid extensions". However with that being said, it is entirely possible (depending on the school and the immigration office) to go from a 60 day tourist visa, 30 day extension, 60 day covid extenesion to a 90 day Non-ED visa

The real question is what did the school you're thinking of enrolling in tell you when you asked them if it was better to go from a 30 day extension on a tourist visa OR a 60 day covid extension to a 90 day Education visa?