Garage Band Musical Typing UI Not showing up

Hey there michaelpaul13,

While you may need to get in touch with the Garage Band experts at Apple Support, we'd like to help rule out what we can first, along with confirming more details to better understand what's happening:

1. When was the last time you were able to use that keyboard combo to show the Musical Typing interface?
2. Sometimes unexpected behavior can be resolved with a restart. Check out the section ‘Restart your Mac' here: Shut down or restart your Mac
3. If you use the other method(not the keyboard combo) listed in this link under the section 'Play a software instrument using musical typing', what occurs? Here's the link: Play software instruments in GarageBand on Mac
4. We see from your post you have macOS 13.0 installed, but the latest version is macOS 13.2. You can verify this by clicking on the Apple logo at the top left corner of the screen, then on ‘About This Mac’. In case you needed it, this link shows how to first back up, then Update macOS on Mac.
5. We also recommend making sure that all apps are up to date: How to manually update apps on your Apple device

Cheers!