I really don't see this being that much different from the famous United States v. Microsoft Corp. case[1].
[1]: https://en.wikipedia.org/wiki/United_States_v._Microsoft_Cor....
EDIT: comments have made clear that Windows had a monopoly on the personal computer space, whereas Apple doesn't have a monopoly on the smartphone or tablet space.
I'm not saying Apple is right to do this. I'm saying the monopoly on their own product is not the correct argument. Apple is not a monopoly. If they lose this case it won't be based on this.
* Contractually barring licensees from offering competing OSes, or selling boxes without Windows installed.
* Leveraging their OS dominance to get dominance in other markets such as linking OS licensing with licenses for other software.
* Pinching competitor's technology using their advantages as platform owner and rolling it into their own products (Stac).
There was more, but those were the main ones.
Such as leveraging their preferred status to get dominance for Apple Music (by being able to charge less since they aren't subject to a 30% Apple Store 'fee')?
It wasn't until the end of the 90s when macs started making an impression on peoples desktops, with the imac, but oddly enough if https://en.wikipedia.org/wiki/Usage_share_of_desktop_operati... is to be believed, windows still has a 95% share of the desktop/laptop market.