Actually, Office 2019 works just fine on both 7 and 8.1... Since Office 2019 shares the same version files as Office 2016 and 365 (which both work on 7 and 8.1), you need to circumvent the artificial block. It just requires a bit of work with some hidden executable.
I would direct everyone to this thread on MyDigitalLife, where user ratzlefatz made a tool to install Office 2019 on 7 and 8.1. In case you need proof, I used it to install it on my 7 VM:
https://forums.mydigitallife.net/threads/how-to-support-chat-office-c2r-download-install-activation.62571/page-14#post-1125229