So if you're outside Thailand the embassies will only give you an ed visa for a university. From inside Thailand you can still do language schools or muy Thai schools.
I mean there's a bunch of different options depending on what your goals are, age, employment status. You could explore education visa options, volunteer somewhere, retirement visa if you're over 50, could find a job somewhere, invest, ext.
Theoretically you could, not sure if you can though. The Phuket sandbox doesn't use ASQ or quarantine hotels, they use SHA+ hotels. You can leave the hotel during the day time. Just look for any hotel that is SHA+