I had to do a double take when reading your comment before realizing that you were probably referring to the Mac version of Portal 2. If that is the case then i

I had to do a double take when reading your comment before realizing that you were probably referring to the Mac version of Portal 2. If that is the case then it's not unexpected, for OSX routinely break compatibility between major versions unless the developer is able to keep up with the changes. This is not to say things are that things are that much better on the windows side. While most 32bit binary run fine in WoW64, driver issues become more common as the games get older. Another major issue is 3rd party services bundled with the games that are no longer available. I can name more than a dozen of games published around 2010 that are no longer available for purchase because the original build depends on the deprecated Games for Windows Live service and would refuse to launch without it installed. Microsoft abandoned GFWL around 2018 and turned off the online installer at a later date so you would have to download an offline installer from some dodgy non-official website. Thankfully it still works with current versions of windows as long as you still have the physical copy of the game, and the backend of GFWL is partially working with achievements still being synchronized with Xbox Live accounts. But who knows how long that's going to last?