Catalina is indeed 10.15. The options are actually "10.6+" and "10.7+", which is severely outdated and not useful, given that everything is going to be 10.7+ anyway. You can look at the system requirements on the store page for the games you want to test and see if the CPU/GPU/OS version are appropriate for that computer, but there aren't really any tricks to make it easier. Anything that's listed on GOG as Mac compatible is 64-bit, but there are some old 32-bit games that won't work on Catalina. The only way to tell is by looking at the Windows system requirements (bizarrely enough) for a note about the Mac version being 32-bit. There aren't very many games yet that need macOS 11 or later, but any that do would have higher CPU/GPU requirements than that machine has anyway. Completely useless post as usual. Whether it's Intel or not has nothing to do with anything. You've obviously never used a Mac and have no clue how they work, so quit it with your weird obsession with trying to "help" people.