Syncing Possible?? — iOS 13 (on 5SE) + El Cap 10.11.6 + iTunes 12.8.2

Asking before I update the iPhone from 10.3.3 (hey, if it ain't broke...), and he needs to communicate with the rest of the workflow. We're REALLY NOT interested in having to shake up a build that's working very harmoniously, but the iOS is clearly past the line of deprecation even though the hardware remains wonderfully functional. I'm not finding anything conclusive here, and I really don't want to lose time in undoing a bad move. My sincere thanks in advance for the wisdom of the assembled.

*In the realm of dreams, I'd very very gladly welcome help towards finding a signed iOS 12 update if that's possible, but extensive web research suggests it's not gonna happen. This seems to have been the ideal phone update for this setup... Thanks again!