iTunes not recognizing iPhone when plugged into computer for backup

Old iPhone backed up to iTunes on laptop (not iCloud).

Purchased new iPhone which I set up using Quick Start (placing phones next to each other). I now want to back up my new iPhone to the laptop but cant seem to do it, it’s not finding either of the phones when plugged in. Looking back I should have backed up my old iPhone to the laptop then plugged my new one in and transferred that way rather than Quick Start. New phone has an eSIM which can’t be reverted.

[Re-Titled by Moderator]