poolast h2rra made a guide on "how to quit half-life 2"
so if you wanted to open half-life 2 again, heres how!

open steam, go to library, search hl2 and then press on the big green button

press the win button, search half-life 2 and then press enter

go to the place where you downloaded hl2 (if you dont know how to do it, just search it up on google)
and then create a cmd file and it should look like this :
then right click on the created cmd file and click on "edit" and then paste in this :
start hl2.exe
and then boom you can play hl2 through cmd

go to the half-life 2 folder
right click on the hl2,exe
make a shortcut
drag it on your desktop or taskbar
boom