I'd pay a visit to your labour department and explain to them what you would like to do. They will talk you through the process. Laws changed a bout 4 years ago ( early 2019) and as long as you're not working in a prescribed occupation, theoretically, you can work for any employer in any province. This, however,is not how it's being interpreted. Seek proper advice from the labour department to stay on the right side of the law.
You have to read the policy to see if it covers COVID up to the required amount. sorry but can'rt really give you a better answer than that. Also, if you're working in Thailand and pay social security, then, I'm quite sure that this will also covet you for the insurance.
it's actually not your responsibility, it's the house owner, hotel, landlords responsibility. If you've never been asked for it then don't worry about it. Some immigration offices won't process anything without it ( Phuket) others aren't bothered. It may be that your accommodation had done it for you and you know nothing about it. Have you had reception ask for your passport and departure card? If yes, then they've probably complied with the reporting requirements.
The fact you got this slip of paper from your hotel in Chang Mai is pretty unusual. As Brett mentioned, looks like they did it in person, then gave you this slip.
Very few hotels will do it this way.
Most will do it on line and give you the screen shot.