Th old games are available if you use the steam depo to download the versions of the game you want.
Tell me the game version you want, and I can give you the exact info you need to get it in less words than it took to write this reply.
I’ve written a couple guides on it in the past, because I get very particular about my gaming experiences sometimes. Most people are oblivios to this option because it is rarely discussed anywhere. However, unless I am mistaken, every update the developer uploads is forever archived and accessable to anyone who owns the game through Steam.
That said, I wish they were all just available in the dropdown list like you provided. It would make things so much more simple.