Can't remove icons from launchpad with an "X" prompt on iMac

Quoting from this Apple Support article:

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

If a Delete button isn’t shown, the app can’t be removed from Launchpad. See Install and uninstall apps from the internet or a disc.

Regards.

Apps that are installed with the macOS cannot be removed.

If you wish, you can create an app folder in Launchpad to keep those unwanted apps from taking up space.

You can also move that folder to another Launchpad page so you don't see it at all on the first page.

Refer to the link that @verjak paw posted earlier for guidance.