Can we report our 90 days report at Koh Phangan immigration office with a TM30?

Well it's like this,

Even with a TM30 showing you're staying at a place in that province the immigration office there (which BTW won't re-open until Jan 2nd 😮 like all offices in the country 😉 ) is under no obligation to let you do your 90 day report there 😕

You can try it with a TM30 and using that address for the TM47 (90 day report form) and it'll either work, OR it won't.

Remember if you have a TM30 filed on you when you travel domestically when you come back to your primary address in Bangkok you'd have to file a new TM30 to show you're back at that address

Try it where you are and report back IF they allow you to report or not