Have you followed the steps to upgrade your Nucleus from 1.8 to 2.0 in this help article (which has been updated since it was first published to reflect the current situation)?
My Nucleus is on line and working.
Can I will use my Mac as a remote again , as it was before?
I just made a big mistake: a reset on Roon Database & Settings. No matter the loss if I get Roon 2.
Once the change is made you will need to update all of your other remotes (iPad and iPhone) but your Mac is on 2.0 so no change should be needed there.
Please keep your eye out, the change should happen any moment since I’ve flagged you for this update. Let me know if you have any issues.