Unfortunately, nothing works. Clicking the "add files" will not prompt any choices but instead Diarium opens straight to Gallery.
Changing the default app also doesn't work.
Miui default apps setting path is like this:
Setting > Apps > Manage Apps > Other Settings (3 dots top right corner) > Default Apps.
Unfortunately doesn't work.
Btw, Miui doesn't have "supported link" option in all apps setting as the google support suggested.