Hi Ivan H! You marked my answer as "solved", thank you, and I'm glad it worked for you!
I can’t remember where I found the Terminal command — somewhere on the internet when I was having problems with Launchpad in Sierra last year. It fixed things for me!
To be clear, Launchpad is an app just like any other, and maintains a database that includes the app icons, where the app is located in the file system, where the icon should be displayed in Launchpad, plus some other bits of info necessary for Launchpad to do its work properly. The Dock is also just an app and, like Launchpad, and by default displays icons (aliases really) of some standard apps plus anything else you put in it. Launchpad and Dock are connected somehow, and this explains the “killall Dock” part of the Terminal command — it resets the Dock too, which is apparently part of the procedure needed to re-set Launchpad, as far as I understand things!
Do a quick Google and you’ll find many articles about Launchpad problems. This one explains things very clearly and also gives you something else to try first if you don’t want to use Terminal!
https://www.igeeksblog.com/apps-missing-from-launchpad-on-mac/
Cheers, Ian.