What settings do I need to review on my iPhone or iMac in order to transfer iPhone photos to iMac Photo app??

In your iMac you should log in with the same Apple ID that you use on your iPhone and set up all settings like this on your iPhone , on your iMac go to photos apps then to photo preferences and make sure iCloud Photos it’s enable and optimize Mac storage selected , then in the General tab select all options and leave the app running in background to sync all your photos to iCloud