How to Fix
Go to your Steam Library / Common / ASTRAL TALE-星界神話.
Rename the folder from ASTRAL TALE-星界神話 to just ASTRAL TALE.
Don’t start the game via Steam Library Play button but instead use the Launcher.exe from the ASTRAL TALE folder, wait for all the updates to finish and the game will start normally without any QT Platform Errors.
The devs will eventually fix this later so until then, just do it like this.
PS: You can also create a desktop shortcut for the Launcher.exe to avoid all this annoying shet, have fun waiting for the official servers to be online.