I suspect Debian is used on more server installs than desktop ones. While it doesn't come with enterprise support options like RedHat it is most certainly used on servers, many of which are in corporate environments and are running multiple services (in containers often) or are otherwise multi-user.
That may be true for Debian itself (although I know a lot of people who have been running it for years as their daily system and still are to this day, including myself for 15+ years and counting), but Debian is also the base for many other distributions, including Ubuntu and its derivatives (like Mint), which are mostly used on desktops rather than servers.
If someone means “Debian and derivatives” then they should say “Debian and derivatives” not just “Debian” IMO, particularly when comparing to RedHat which also has a number of significant derivatives.
TBH I've always considered Ubuntu (and by inference its derivatives) more of an “inspired by” in relation to Debian, given it is generally closer to Testing then Stable and has many notable changes on top, more so as bigger changes have increased over time (snaps being so ingrained that they are almost required, for one).
I suspect Debian is used on more server installs than desktop ones. While it doesn't come with enterprise support options like RedHat it is most certainly used on servers, many of which are in corporate environments and are running multiple services (in containers often) or are otherwise multi-user.