How can I troubleshoot or fix when macOS Photos app import from a connected iPhone gets stuck on "Preparing to import from..."?
How to get the photos to appear for selection in the macOS Photos app after only waiting 1-2 minutes

Disconnect the iPhone.
Close the macOS Photos app.
On the iPhone, open Settings.
Select Photos in the Settings App of the iPhone.
In the &quot;Transfer to Mac or PC&quot; section of the Photos settings, Automatic is the default. Change it to Keep Originals.
Open the macOS Photos app.
Reconnect the iPhone and select the device in the macOS Photos app.

Keep Originals Setting

Source:
Photos 'preparing to import from iPhone' message....