adding an app to launchpad in macos catalina

Hmm.. as far I know that is the correct way to add an app in Catalina. I assume it is in your Applications folder and is not an AppStore app which should be automatically added?

Use Launchpad to view and open apps on Mac - Apple Support

You might try doing the same drag while in Safe Mode:

Use safe mode to isolate issues with your Mac - Apple Support

Provided the application does not already exist in the Launchpad display of applications, then dragging and dropping its application icon onto the Dock : Launchpad actually does add it to the Launchpad. Tested: Catalina 10.15.3.

If you want to remove a specific application from Launchpad, then combine control+option+command keys to get all of the applications wiggling, and then specifically click the ⓧ on the application you want gone from Launchpad.

You're welcome. Yes, it can be as many pages as you have apps. If you want alphabetical order by name you can launch them from your Applications folder. You can also drag your Applications folder down to the right side of the dividing line your Dock.

Find the app in your Applications folder and drag it to the Launchpad icon in your Dock.

You are welcome.