I don't work for JRiver, so this is my own personal opinion on the subject. If a user decides to keep using a Windows operating system that's not supported by Microsoft anymore, I wouldn't expect third-party software vendors/developers (including JRiver) to go back and try to support those dead Windows OSes anymore. Basically, in my personal opinion, you're on your own when choosing to stick with a dead OS, even though Windows 7 and Windows 8.1 users can still right now upgrade to Windows 10 for free. There are some hardware vendors including Nvidia, Intel and AMD (in regards to GPU drivers) that have dropped official Windows 7 support from their drivers. Bottom line is, the way I see it Media Center 26 does work on Windows 7, but because of how old Windows 7 is (and it no longer being supported by Microsoft), it may or may not have what's required to support newer features in Media Center, including the newer versions of theater view powered by OpenGL/ANGLE.
That said, I did mention a search of the forums might yield some information that *might* get it working. For example, this post from Hendrik from nearly a year ago regarding Windows Updates needed to get it working:
https://yabb.jriver.com/interact/index.php/topic,120042.msg833877.html#msg833877In fact, that entire topic might be illuminating on this subject. But I wouldn't expect newer features (especially video-related features) to keep working in Windows 7 as new, major Media Center versions get released. Honestly, I wouldn't be surprised if Windows 7 support is officially dropped by JRiver within a year, maybe two at the most. Regardless, I hate to be that guy and point out the obvious but for the sake of security alone, I wouldn't recommend
any user to keep using Windows 7 right now, especially when those users can still upgrade to Windows 10 for free (or if Windows 10 is less than desirable, I'd recommend jumping to a Linux distro like Ubuntu or Manjaro).