iMac unable to run Roon 2.0, need assistance moving Nucleus to 1.8 Legacy

It can be fixed. There is a version of 1.8 that’s been released. It’s 1.8 (Legacy). You need to download that and run the install on your core (always do a backup) and then download 1.8 (Legacy) software on all your other devices.

Here is some reading

If you get stuck we are all here to help.