I'm not a tax expert, but in most countries, taxes are calculated based on the calendar year. For instance, if you spend 10 months in Thailand (from August 2024 to May 2025) spread across two calendar years without meeting the residency requirement of 180 days in either year, you may not be considered a tax resident.
Under the current law, you only pay taxes on the money you bring to Thailand when you stay more than 180 days/calendar year.
Technically speaking this should be applied to most long term visas and you should pay taxes under other visas too (unless its a tax exempt visa) . But I think the Thai gov will enforced on the DTV more.
If you don't want to pay. just stay less than 6 months/year.
It works very well for a nomads who wants to travel multiple countries during the same year.