I think they wont be able to account trf even tho windows and steam actually use same launcher.

The Free Trial is available in Indonesia but not full game, i can still purchase the windows version but wont be able to use my character on steam, since need to make new account for that.

Again best solution i have is to keep my Steam Store in Japan to be able to purchase. I find a thread with similiar problem with me,

https://forum.square-enix.com/ffxiv/threads/444014

sadly the OP still not responding to my question about their Steam Store status, but it seems they revert their store region preferences to Indonesia, well mainly bcs of regional pricing.