No, it is not tax free. The country is a tax hell when it comes to crypto!
Thailand considers crypto to always being with you. Therefore it is irrelevant where you buy/hold/sell your crypto - it is always "onshore" for Thai tax purposes. And Thai tax rates are quite high .
Read this -> Best country for a crypto hermit? (post #10).
TH has no CFC rules tho so if you trade crypto through a foreign company and then the company pays you to a bank account outside of TH then the 1 year remittance applies.