as far as taxing foreigner on overseas remittances they have never done it before, remember they have a new government now and sometimes a new broom sweeps clean. May be there will be a U-turn but as of today there is no sign of that.
Boaz, there are many things we are struggling to work out how to comply with this, the Thai gov has a habit of this kind of thing. You are required to work out what you owe and pay it. There is a 200% penalty for not filling.
/FOREIGNERS_PAY_TAX2024.pdf you need also to consult the relevant DTA. https://www.rd.go.th/english/766.html additional you have some in country allowances. https://www.rd.go.th/english/766.html please share as many are not aware or still in denial.