Thank you, in particular for the comprehensive compilation of the relevant documents in one place.
With regard to my question to BoI on the requirement to submit a tax declaration: I asked the question when I was in BoI office on the day the LTR was issued.
You get this minder and she goes through the documents with you and guides you through the different steps on that day. So she had all documents on my financial situation including (no) income in Thailand, foreign pension, assets abroad,..
I explicitly asked her 2 questions for confirmation: a) does the LTR "wealthy pensioner" exempt me from being taxed in Thailand and b) do I have to file a tax declaration.
The minder sat down with me and took her time and didn't rush it through. Her answer was on a) a clear "Yes" and on b) a clear "No". With regard to my question on the tax declaration there was no hesitation or constrains in , "like not for this year" or "as long as you don't bring funds into the country,..".
That was in March this year.
Anyhow, for 2024 I didn't transfer any funds into Thailand and only used local credit cards. So there was/is no foreign income transferred into Thailand in 2024.
For the future I planning to only transfer funds that I owned pre-2024 to support my life in Thailand. As most of my assets are investments in stock markets it's a bit of a nuisance to distinguish between assets owned pre-2024 and assets bought from income that I earned later on, in particular if I buy/sell share.
If someone has guidance on how to prove/document that money transferred into Thailand comes from "old (pre-2024 assets)" versus "new" income, please let me know.