Can I apply for a Digital Nomad Visa (DTV) while in Thailand on a tourist visa?

The Lawyer is absolutely correct. You must be outside of Thailand and apply online. You will be asked to provide evidence of the location that you are in to make your application. Including copies of your passport pages, showing the entry stamp into whichever country you apply from. They will also most likely ask for pictures of all passport pages including blank pages a few days into the application to check you are still in the same country. Do not try and do anything else or your application will be rejected, and you lose the visa fee

absolutely right...must be applied outside Thailand.

A lot of embassies will ask you for proof showing you're in the country where you're applying. A friend of mine was asked to show receipts for stuff he'd bought around Hanoi.

You actually can get refuse to entry for a year or so if you will be in thailand when waiting for DTV.

Yes it’s true

He's correct.

You can “begin” the request in Thailand but you can’t “submit” it until you’re in the country you’re applying through. They’ll want proof that you’re actually there and can call you in for an interview at short notice.

You can't apply for a DTV from inside Thailand. You need to travel to a nearby country, apply for the DTV at the consulate that serves the area you travel to and remain there until the application process completes

True, you cannot be in thailand when you submit your application. They want proof of your physical location outside thailand