How can I get my iMac to trust my MacBookPro

A trusted device is fully signed into your Apple ID and is able to receive Apple ID verification codes. I would suggest making sure your MacBook Pro is all the way updated, and ensure there are no alert messages in the System Preferences app [on your MacBook Pro] asking you to "Update Apple ID settings" or any related messages.

Hey TheOldFart,

To add a trusted device to your Apple ID, take a look over the tips here:

• Check your Apple ID device list to find where you're signed in - Apple Support

"Add a device to the list

To add a device to the list, you need to sign in with your Apple ID. After you sign in on a device with your Apple ID, that device appears in the list. Here's where you need to sign in:

• For iOS or iPadOS, sign in to iCloud, iMessage, FaceTime, iTunes & App Stores, or Game Center on the device. You can also see your paired Apple Watch.
• For macOS or Windows 10 and later, sign in to iCloud on the device. 
• For Apple TV HD and later, sign in to the iTunes and App Store on the device.
• For Apple TV (3rd generation) and earlier, sign in to the iTunes Store on the device.

Your AirPods will appear in the Find My app, but they won't appear in your Apple ID device list. You can remove your AirPods from your account using Find My. Devices running iOS 7 or earlier or OS X Mavericks or earlier won't appear in your device list."

Cheers!