How to get rid of file in Launchpad?

That's an App folder. If you need to get rid of it, move the contained apps out of it.

Click on it once to open the folder, then simply drag one of the icons out of it.

You don't want to delete the apps if you use the mentioned Adobe Illustrator.

If you no longer use Adobe Illustrator, then uninstall it according to its own instructions.

https://helpx.adobe.com/creative-cloud/help/uninstall-remove-app.html

Check to see if you have this controlled on or off. Go to settings then go to accessibility. And then go to switch control and check your settings there. Perhaps that is what is blocking your ability to change anything. The only reason I mentioned this is you said it’s in launchpad? Under switch control there are many settings, which allow you to control what you do and behaviors that you are speaking about like pressing it holding button to get rid of an app or file I hope this helps :-)