you’re referring to the TM6. It has been suspended for air travel.
Joe is referring to the TM30. Which is done by either the hotel or landlord of the condo etc you’re staying at. You can also do it yourself. It’s required within 24hrs of being in Thailand.
Bangkok immigration doesn’t ask for it, the TM30. If you can get it, I would suggest you have it. Just in case.
The tm6 has been cancelled for now., for air traveller’s only. No worries about that. In Chiang Mai, you’ll need the tm30. Bangkok immigration doesn’t ask for it.
I would contact your airline to make sure they’re going to allow you to board the plane. Some airlines will not allow you to board without proof of onward travel out of Thailand within the initial 45 days.