Extension greyed out in the latest Photoshop (Windows)

I just installed Photoshop 2026 on my new laptop (Windows 11) and when I tried to install a third party extension, I found that the Extensions is greyed out.

I followed some posts on the Internet to check in the Preferences, but the extension panel option is enabled already. I also tried to uncheck and recheck, then restart Photoshop but it didn’t work. I then tried to upgrade the Photoshop to the latest verion via Creative Cloud Desktop, and also uninstall and reinstall, but it still not available. Would really appreciate any suggestions or guidance!

Thanks in advance