Sync Session Failed to Finish (May 2021 Edition)

Hello again, the good old "sync session failed to finish" (SF2F) issue is back in town.

There are many temporary solutions discussed in this forum, but eventually the error comes back after some time. Here is what happens:

When the iPhone is connected with an USB cable to a Mac, it begins the wired sync procedure in finder.

The last sync step "Backing Up" seems to take somewhat longer than expected.

After that, the "Backing Up" process restarts again and immediately terminates with well-known the error message:

"The iPhone (name) could not be synced because the sync session failed to finish".

There is no event log nor a meaningful error message that could be used to track the underlying root cause of this recurring issue.

With the USB cable still connected, pressing the (Sync) button in Finder syncs again, with no error message.

After disconnecting and re-connecting the iPhone with the cable, the error is back. Syncing without the cable (over the air) seems to work only temporarily after the Mac was rebooted.

After some working hours, wireless sync is then no longer possible (Finder gets stuck with "Waiting for sync to start" and then terminates with the error "sync session failed to start.")

This issue has been around basically since the early days of Big Sur and it would be highly appreciated if sb. would come up with a sustainable solution.

Temporary solutions are: rebooting the Mac and the iPhone, turning iCloud Photos on/off, restoring the phone from a previous backup etc.

These solutions consume a lot of time, keep users busy, and may all work for a certain time. But eventually the error comes back after a couple of days.

Anyone from Apple reading this and considering a bugfix to relieve users from this nuisance would be highly appreciated.

Thanks in advance!