Can I switch from a work visa to a DTV visa while teaching online in Thailand?

The fact you want to do it doesn't seem material. You would need to set up a company, have contracts with students in your company name, generating income, show that in your company accounts. Many embassies will want to see your company registration and some want to see a tax return from your home country showing the company is legitimately earning.

You can't use students or financial information pertaining to your thai employment for this. So you may be able to do this in the future but I doubt you could right now

Do you have your own company or working for a non-thai company? Screenshot of your customers and spreadsheet of your income? You need a company and invoices.

And maybe you will have a big problem if you go this path, if they see that you have a working vidlsa and work... Be careful. Better to find another solution.

Do the soft skills version and keep Thailand out of your business.

I'm not understanding something here. You want to use the students and income that you get from your current visa and work permit to apply for the DTV? I don't see how that could possibly work. What am I missing?

If you are currently only working with European students online, how do you have a work permit?

Can only get the DTV for work outside of Thailand. A letter from your company that you work remotely and for a Non Thai company with non Thai students/clients.