There's a lot of controversy over that visa at the moment. Apparently, although it's valid for 5 years, you've still got to leave Thailand at least twice a year.

I think the most concerning thing about the Destination Thailand Visa is that the Thai embassies and consulates seem to be interpreting the rules differently.

I honestly think the whole thing is a bit misleading. It’s marketed as a visa for (and I quote) ‘digital nomads and remote workers who want to live in Thailand legally!’ But if you examine the small print, it’s clearly aimed at employees, not freelancers. You’ve gotta show half a million baht in your bank; proof of income; 6 months’ worth of pay slips; a sponsorship letter; a ‘foreign employment contract or employment certificate authenticated by the embassy of the country where the company is located’; a ‘copy of the company’s registration/business license authenticated by the embassy of the country where the company is located’; and a ‘professional portfolio showcasing digital nomad, remote worker, foreign talent or freelancer status’!

If you haven't got a job in Thailand already arranged before you arrive in the country, it's probably best to come in on a tourist visa (there are different kinds, depending on how long you want to stay) and if you do get a job while you're here, get the tourist visa converted into a non-immigrant visa at an immigration office, so you can then get a work permit.

So useful! Thanks for all the replies!