I attempt to sync a 2020 iMac 5K to a iPhone 15 Pro Max (via USB-C). I do have an Apple Watch Ultra connected to the iPhone.
I've found that the first attempt to sync always hangs - whether the iPhone is configured to sync to iCloud or the Mac.
After the sync hangs, disconnect the USB-C cable, wait for animations on the iPhone to finish, and reconnect the USB-C cable. The next sync will succeed as will subsequent syncs until (I believe) you reach an idle time when the iPhone would require a passcode again. That sync will fail, but you can do the disconnect/reconnect shuffle and get it working again.
I keep a lot of media on-phone which is why I sync from the Mac to iPhone.
This is really annoying since it can put up to twice the wear on an already more vulnerable (and hard to connect) USB-C connector.
For some reason, the USB connectors have always been a female connector on the male side (housed in a high tolerance sleeve for USB-C) making the connector harder to align than lightning - which is why there are no docks or alarm clocks featuring USB-C. Blind docking just isn't a practical solution with USB-C.