Dorico version:5.0.20
iPadOS version:16.6
I tried reinstall the application, reboot the device, none of these works.
Is this a brand new file that you just created on the iPad, or did you try to open a file that had a custom music font?
This is a new file, but existing file cannot be normally displayed even it can be normally displayed in older version (<5.0).
Can Dorico for iPad produce a Diagnostic Report? (IIRC it can from one of the right-hand menus.)
That would be a great place to start investigating if @winicu can post it here.
If you reset the music font via the application menu at the right-hand end of the toolbar, does that help?