I_use_mac_m3 wrote:
Isn't it because it used to be available on mac?
If Valve ever distributed a version of Team Fortress 2 for Macs on physical media (optical discs), that would have been long, long ago. Very few developers still distribute software that way.
If such a version even exists, there's an excellent chance that it would have been written using 32-bit code; code that does not run on current Macs (or even on Intel-based Macs running Catalina or later). (More on this below.)
As far as downloading it directly from the developer site,
https://www.teamfortress.com/freetoplay/ says

The certainly implies that there is a Mac version – but when you click on this button, you're taken to the listing in the Steam Store, where there is no tab for macOS, implying that there is no Mac version. At least no version that is still available. Maybe there used to be a 32-bit Mac version and the developers withdrew it because they knew the code wouldn't run on Catalina and later, and they haven't prepared a 64-bit or Apple-Silicon-native replacement.
https://en.wikipedia.org/wiki/Team_Fortress_2 indicates that that there was a macOS version of Team Fortress 2 – one released in June 2010. Back then, Mac OS X 10.6 (Snow Leopard) was the latest Mac OS. Snow Leopard was the first version of the Mac operating system to implement full 64-bit support, so while the game developers could have written that old version of Team Fortress 2 as a 64-bit application, chances are that they didn't.
The Mac App Store didn't exist until Mac OS X 10.6.8 came out in June 2011. So that ancient Mac version of Team Fortress 2 would likely have originally shipped on optical discs (CD-ROMs or DVD-ROMs). I see no sign that Team Fortress 2 is in the App Store now – so either it was never there, or the developer pulled it.