Cannot backup my iPhone to my iMac

Pocket lint in the port can be an issue.

A compressed air blowout or a very gentle sweep of the port with a toothpick may remove anything lodged in it.

And I'm sure that Apple suggest that you never ever put anything into the port that isn't a cabe, so you do this at your own risk.

Most of the time that has been attributed to a bad or flaky cable, more often an Apple cable than not.

That would seem to preclude that Rod.

You're welcome. Happy to help.