Hi Kaeul,
The AI Answer already covers the most common cause, so I'd start by checking whether the Text Input Management Service is running and whether the Chinese IME appears under the language's Keyboards section. Since the language shows in the taskbar but selecting it does nothing, that remains one of the most likely causes.
If those look correct and the issue persists, try creating a new local user account from Settings > Accounts > Other users > Add account. Sign in to the new account, add Chinese (Simplified) and Microsoft Pinyin, then test switching languages with Win + Space. If it works in the new account, the issue may be limited to your current user profile.
I'd also check for Windows component corruption. Open Command Prompt as Administrator and run:
DISM /Online /Cleanup-Image /RestoreHealth
sfc /scannow
Once both commands finish, restart the PC and test the Chinese IME again.
Finally, please run winver and share the full Version and OS Build shown in the dialog. Since you've had this issue for about a year and it affects both Microsoft's Chinese IMEs and third-party IMEs such as Sogou, the exact build number may help determine whether this is a known 25H2 issue or something specific to the installation.
I hope this helps point us in the right direction. Feel free to post back with the results and I'll help take a closer look from there.
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