PianoMonk I bought Finale and Sibelius back in 2009, no subscriptions, own them outright, to run on Windows XP. I never updated either of them, because they both do what I want them to do - allow me to write out a score.
When you say "own them outright" .... Back in the day when I bought MS Word for my business, I got a CD and when I had to replace my computer, I simply could install the suite again via the CD. At some point I lost the CD and also didn't have proof of ownership and so had to "purchase" it again, but that was by subscription which has to be renewed every year. I've been stuck with that and the "upgrades" making it function less well ever since.
Finale, I didn't get a CD for installing - it was done on-line. I do own it outright as well. When I replaced my computer (because it was failing), I could reinstall it for free - but it was via the site. I hate upgrades because usually they involve bells and whistles of unneeded things, so I don't care about that. The way I understand it, if in some future time I need to replace my computer, I will not be able to reinstall Finale, because the site for reinstalling it (for free) will be gone. In your case, if you got a new computer, could you reinstall (do you have something like my CD for the original MS Word?).
I didn't know we were able to stay with the old Windows XP. I have Win11 which came preinstalled when I had to replace my computer. The same happened with a friend, and I seem to remember that Win11 messed with the older Finale.