What visa options do I have for backpacking and studying in Thailand as a Dutch citizen?

Get a 60 day tourist visa to come in on, and do your traveling around, but be sure you make personal contact with the university you will be studying at at least a month before you start school so they can get all the paperwork together that you will need for your ED visa. It usually takes a few weeks for them to get everything together, and the approval back from the education ministry. To do this you will use the immigration office in the district your university is in. The borders are back open now so a jaunt over to Vientiane and the Thai embassy to get your ED visa could save you about bt of that mentioned bt20k fee to change it in-country. The return to Thailand would simply be the same, but new, ThaiPass you originally entered on, with the covid insurance and your vaccination records. It will take two days to complete. You turn in your application and documents, then the next day you pick up your new ED visa in your passport. Just make absolutely sure you physically contact the school after you get here, and get your education fees all paid. That is very important, or you won't get your ED visa on time.

You can study on a tourist visa or whatever you're on now. You can get an ED visa in country, normally there's a $20k baht in country conversion fee. Depends on the school and immigration office though.

get 60 day tourist visa (extendable once) once inside see if you can convert it to ED Visa