It looks like Apple has updated the Technical Specifications for the iPhone-15-family phones.
If I remember correctly, when Apple first published those specifications, they said that on High Sierra or Mojave, you needed iTunes 12.9. There was no 12.9 at the https://www.apple.com/iTunes site.
Now the specifications say 12.8, suggesting that the 12.9 was an error. Perhaps that's the version that's built into Mojave, and whoever wrote the initial specifications didn't realize that the version for High Sierra was different.
In any case, now that the specifications refer to a version that is readily available, and there are reports (here) that (under some circumstances, anyway) iTunes will update itself to handle iOS-17-based phones, maybe things are starting to look up a bit.