downloading photos to iMac using MacOS Monterey

A Mac with macOS Big Sur 11.1  or later is compatible with Apple Pro RAW. So your iMac with Monterey should be compatible and and able to download them. You may have difficulties to download the photos however with Image Capture or Photos and see an endless "Preparing", if you have iCloud Photos enabled n the iPhone or if the iPhone is used as a personal Hotspot. If you are using it as a personal hotspot, turn this off, while transferring the photos. And if your iPone is syncing with iCloud Photos, download the photos from iCloud rather than from the iPhone, as the iPhone is only mirroring them.

Apple recommends to transfer the Apple Pro RAW photos to your computer using iCloud Photos. It is the easiest way to transfer the RAW files to a computer, see the paragraph "Share ProRAW photos": About Apple ProRAW – Apple Support (UK):

"Here are the best ways to share your ProRAW photos:

• Use iCloud Photos to access the original ProRAW file in full resolution on all of your devices.
• To transfer the original ProRAW file from your iPhone to another iPhone, iPad or your Mac, use AirDrop. If you edit the photo in the Photos app and then share it, you'll share a JPG file. To share the original ProRAW file from the Photos app on your iPhone, tap Share, tap Duplicate, tap Edit, tap Revert and then share the photo using AirDrop.
• To share an edited ProRAW photo with someone else, edit the photo in the Photos app on your iPhone, then AirDrop, email or send with Messages. A JPG file that includes your edits will be shared.
• To email a ProRAW photo, create an email in the Mail app on your iPhone and then add the photo to the email. The Mail app converts the ProRAW file to a smaller JPG file automatically, which you can then send by email.
• If you edit a ProRAW photo and want to share both the original ProRAW file and the edited JPG file, use Image Capture on Mac or the Windows Photos app on a PC to import the files. You can also use AirDrop to share both files to a Mac. Tap on Options and turn on All Photos Data before sharing, then select Save to Downloads when you receive the files on your Mac.
• If you edit a ProRAW photo in the Photos app on your Mac, and you want to use your Mac to share the original ProRAW file only, select the photo in the Photos app, then choose File > Export > Export Unmodified Original."
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There currently is a known issue with "Preparing to import" taking forever. You can search in the discussions and see lots of frustration. Some people have had success with toggling airplane mode on their phone. That did not work for me.

What did work for me is booting my Mac in safe mode. Once of the things safe mode turns off is HW acceleration, so it took a while (about 3 minutes) to finish "preparing" before the photos came up. Once I booted back without safe mode turned on, it must have unclogged the pipes because everything works normal now.