I think regular anti-trust laws would be the way this would be fought on the desktop.
macos as a whole doesn't have enough users in the EEA to fall under the purview of the gatekeeper section of the DMA, unless the "app store" counts as a single thing. Which it kind of does now that apple has unified it between iOS, iPad OS, and macOS.
Windows S versions that only allow software from the microsoft store haven't drawn any ire from EU countries, AFAIK.
macos as a whole doesn't have enough users in the EEA to fall under the purview of the gatekeeper section of the DMA, unless the "app store" counts as a single thing. Which it kind of does now that apple has unified it between iOS, iPad OS, and macOS.
Windows S versions that only allow software from the microsoft store haven't drawn any ire from EU countries, AFAIK.