How can I restore missing actions in the Shortcuts app?

Creating this as it might be helpful to other users, but this is resolved for me.

I restored an iPhone Se 3rd gen using a backup of an iPhone 12, and immediately noticed the list of available actions was extremely low. I couldn't run a shortcut, get network details, or even send a message. Weirdly, coping over a shortcut would work and it would run as usual.

Apple Support couldn't figure it out, but suggested I reinstall the Shortcuts app, among other options. In my case, the reinstall seems to have done the trick. I opened the app, searched and initially saw nothing. But after a minute or so the full list appeared and is working.

Hope this helps!

[Re-Titled by Moderator]