Hello @Frambooisier, several goldsrc games share game content and need to be installed in the same Steam Library to work properly. Steam is forcing those specific games to use the same library so that you're not left with a broken game install.
If you want to change which library they're installed in, then uninstall the other goldsrc era games and Steam will let you select a different Steam library folder.
Thank you, quite logical.
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Your system information
Please describe your issue in as much detail as possible:
There should be option to select to witch steam library a game should be installed, for some game there is for some not.
Steps for reproducing this issue:
https://user-images.githubusercontent.com/15931041/210279176-8ca54405-05a3-419d-9023-6b4ab57f73ee.mp4