how to rename applications in "show apps", such as "GNU Image Manipulation Program" to "GIMP" 20.04.2?

Solution 1:

cp /usr/share/applications/program-name.desktop $HOME/.local/share/applications/

Open the copied file, search for string name and change the name there.

Solution 2:

With the little tool alacarte ("Main Menu"), you can edit the launchers:

You need to install it first:

sudo apt install alacarte

alacarte screenshot