You use the address of the hotel where you are staying in the country you apply in. A receipt from the front desk or a screen shot of your online booking is the proof.
If you already live in Thailand you should take a trip a nearby country and apply to the Thai embassy after you arrive and have the stamp in your passport.
Did this person submit evidence of income earned as a remote worker as part of a DTV application? Is that how they were caught for not paying Thai income tax?
You need a record of making money from remote work to apply as a digital nomad. You could sign up for a soft power activity and get the visa that way. You can still do remote work and try to earn money later. If you have enough savings to live for years then the activity fees will be very affordable.