Good afternoon dwyhelp,
Welcome to the Apple Support Communities!
I understand you are trying to sync your contacts between your iPhone 8 Plus and your iMac. It looks like you've updated your iMac to macOS Catalina, but have you updated it to the most recent 10.15.2 version? What iOS version is your iPhone running? It should be updated to iOS 13.3. Once the devices are updated, restart the computer and iPhone to refresh them and reestablish a connection to the internet.
The easiest way to keep your contacts synced between your devices is to enable iCloud. If you choose to sync to your computer with a USB cable, Finder has replaced iTunes as the application to manage data. Take a look at the resources below:
What happened to iTunes?
Change your iCloud feature settings
Use the Finder to sync your iPhone, iPad, or iPod with your computer
About the 'Trust This Computer' alert on your iPhone, iPad, or iPod touch
"If you tap Trust or Don't Trust but doesn't accept your answer, or if the Trust alert won't appear, follow these steps. Try again after each:
- Make sure that your computer has the latest version of maOS or the latest version of iTunes.
- Disconnect and reconnect your device from your computer.
- Restart your iPhone, iPad, or iPod touch and your computer.
- Reset your Trust settings.
If the above steps don't help, go to Settings > General > Reset and tap Reset Network Settings. This also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you’ve used before.
If you downloaded iTunes for Windows from the Microsoft Store, make sure that iTunes Mobile Device Helper is enabled as a startup item.
If you still need help, contact Apple Support."
Take care.