can't update iphone to ios 15 requires windows 10

I went to upgrade my iphone xr to ios 15 with itunes. Itunes said i need to upgrade to latest itune. itunes upgrade said can only be used on windows 10, I use windows 8.1 I like it, it's fast and I don't have to worry about all the privacy crap.

I can upgrade without useing itunes but then I would not be able to access my iphone with itunes for backups or music.

Am I missing something?