How do I move photos from my iPhone 12 to my iMac photo library?

Connect the iPhone to the iMac with its USB cable and Photos should open. Go to the Devices section in the Sidebar and click on your iPhone. Then click on the Import All New Items button:

Brand new Mac Air and Iphone 12 Pro here. I cannot make the Mac Air Photos app download the pictures from the phone. I tried Image capture too and it is blocked. It doesn't let me do it. I seriously do not know what to do. I have Icloud subscription for 200 Gigs and I don't think the pictures will fit, so I know that is not going to work. I updated the systems (both iphone and mac), I already checked the preferences and nothing. They do not speak to each other.

my iphone pics have peg file which will not import to my imac

Use Image Capture to download those problem files to a folder on the Desktop and see you you can open them with Preview.