Hi,
I just find about this program and your question!
This program doesn’t have a launcher, you have to launch it from your terminal. I’m using Lubuntu, and never used Pop!_OS, but it should work the same…
Open your terminal, usually Ctrl+Alt+T, then enter the folder where you extracted left, for example:
cd ~/Downloads/left-linux-64
Then launch the app using ./ before the name of the file, in this case:
./Left
Left should open.
Most programs will run using this prefix ./
I think the programmers should incorporate the launcher, to let it more easy for the new users.