After selecting EU region to enter the game on the Battle.net client, the in-game region option is locked in CN without any other options, resulting in the inability to log in normally. But I can log in to the EU server without any problems when playing Overwatch.
I have tried several methods, including reinstalling the Battle.net client, reinstalling StarCraft 2, and setting up a new administrator account for my computer, but none of them have solved the problem.