You have to understand as time passes, support for older (and unsupported) operating systems has to be dropped in newer versions of the software. When that was said when Windows 11 was released in 2021, it was just a year after extended support ended for Windows 7 and it was for an older version of Media Center (maybe MC28/29/30?) that was current at that point in time. Lots of software has fully dropped support for Windows 7 including popular apps like web browsers, games, etc. This happened with Windows XP and to Windows Vista. It's happening with Windows 8 now and it'll happen with Windows 10 too, since Microsoft ends support for it in October, but it likely won't be an immediate dropping of software support from software vendors. There's usually a few years of leeway before software vendors (like JRiver, Google, etc.) fully drop support for it. I can't recall when JRiver changed the system requirements officially dropping Windows 7 support, maybe for MC30 or MC31 or maybe MC32? Regardless it was a few years after all support for Windows 7 ended from Microsoft.
It's not feasible to keep supporting older operating systems after a certain amount of time. While I think JRiver has done well supporting Windows 7 and Windows 8 longer than most other software vendors have after Microsoft ended all support, they can't simply keep supporting it forever. Supporting it longer adds development time (which time is money) and requires having, using and maintaining older hardware for testing and development of those older operating systems as the user base dwindles (and yes, I'm aware it could be done in virtual machines without needing dedicated older hardware, but that's a different rabbit hole). And of course there's technical reasons for dropping support as well, for example features only available in newer operating systems are not available in older ones like Windows 7 and of course drivers for devices like GPUs dropping support for older operating systems as well.
IMHO, Jim/JRiver, I think it's close to being time to drop Windows 8 as well on the system requirements page too. Microsoft ended extended support for it in 2023 and its user base is much, much smaller than what Windows 7 was (and I guess still is for the holdouts). I don't think it'd cause too many issues dropping it too, but then again I suppose I could be wrong in my thinking. Also then again, you guys did support Windows 7 a few years longer after Microsoft dropped support so maybe Windows 8 has a year or too left for you guys?

I actually would be interested in doing a poll or something about if users are still using Windows XP, Windows Vista, Windows 7 and Windows 8/8.1 and see if they plan on running it to the very end, switching OSes (Windows 10, Linux distro, etc.), replacing with new hardware (Windows 11 PC, Mac, etc.) or something else altogether.