It tries to redirect to https://education.minecraft.net/zh-hans, but it actually redirect to https://education.minecraft.net/en-us/error/404. (May be it because I was trying to access it in China.)
As the image shows, there is something wrong with the website.
I am confirming this bug in version 1.21.124 Hotfix (Windows 11 25H2), and it has become more severe.
Test Results:
Standard Double-Click Method (Game Closed): Double-clicking an
.mcaddonor.mcpackfile launches Minecraft, but no import notification appears. The pack is not added to "My Packs".Original Workaround (Game Closed): The reported workaround of closing the game before importing no longer works. The behavior is identical to point 1.
Manual Installation Method: After renaming the file to
.zip, extracting it, and copying the folder to the correctcom.mojang\\behavior_packs(orresource_packs) directory, the pack does not appear in the game's Settings > Storage section. It is completely invisible to the game.Conclusion: All known methods of installing add-ons (double-click import and manual file copy) are currently non-functional in this version. This completely blocks add-on usage on Windows.