Reserve your place at a recognised government licenced school under the ministry of education. Pay the semester fee and you will receive a temp under consideration ed visa. After 3 months of attendance it will be confirmed and as long as you attend regularly and make progress you won't have any issues.
I heard that if you had the correct paperwork you will be able to get a new non b at the border without leaving Thai territory so other requirements won't apply
I visited immigration today with the same issue. Here is a copy of my understanding. Immigration say that when old school cancel work permit they will give me a letter. I must take that letter together with new work permit. Criminal records check and teacher licence to immigration. They will cancel old non b and issue new one. I should do this before July 31st or if amnesty extended the new end date. There is no need for me to leave Thailand as I have been throughout the Covid 19 matters and to do so would expose me. They also say i can cancel visa myself, get an extension which will be valid until visa amnesty finishes and then do a border crossing for a new non b visa
What about if you have a non b and a work permit (non b already extended for 12 months) and your old employer cancels your work permit and then your non b is automatically cancelled. Are you on amnesty?
Repatriation flights 4 or 5 times a week. Return flights minimum and you need impossible documentation to return and 14 day quarantine at your expense. I would stay here for the moment. Its safer.