How do I rename an app in MacOS properly? I am trying to rename an app in MacOS. I tried it using Finder, navigating to Applications, right clicking on the app to rename, moving to "information" and renaming it there.

This works in most places where the app name appears, but if I have the app opened in fullscreen and I swipe up with 3 fingers I still see the old app name in the menu at the top of the screen.

How can I change the app name also there?
Renaming the .app package in Finder only changes the name there, it doesn't change the name shown in the menu. To do so edit YOUR.app/Contents/Resources/XY.lproj/InfoPlist.strings (with XY being the language you are using) and change CFBundleName there.

For applications without localization files you can also edit YOUR.app/Contents/Info.plist and set a new value for CFBundleName there.