I apologize for my terminology because it probably wasn't accurate or that clear.
While using your existing Apple ID or iCloud account, open Calendar, then go to File > New Calendar > iCloud. Give it a different name and color than your existing calendar for troubleshooting purposes(you can always delete the old one and rename it and change the colors later). Once the new calendar is created, try creating a new event under it to make sure that it syncs across all of your devices. In my scenario, doing this revealed that the new calendar synced correctly while the old one continued to show an error icon.
As far as migrating the calendars, I think there are two options. Luckily for me I didn't have too many events so I went into each event and edited them at the bottom where it indicates which calendar you want to associate the event with. The other method that I was going to try, but wasn't sure if a corrupted event/setting would carry over to the new calendar if I did, was to export my old calendar to my desktop, then import it back into my new calendar. Theoretically, this should move all of those previously entered events under your new calendar without having to click into each event like I did. Because I've never tried it, I can't speak to whether or not the original error would return. *However, if your Mac Calendar is empty due to syncing issues, the export method won't be of much help as it only exports what is currently visible in that calendar. But if your calendar currently contains all the events you'd like to keep, but it just can't sync anymore, then exporting and importing might work.
If you decide to try the export/import method, it's pretty straightforward. After you create the new calendar, click on the old one and go to File > Export. Save the file to your desktop, then go to File > Import. Choose the file you just saved and select the destination as the NEW calendar you just created. Again, theoretically, it should work.
I followed your clear instructions and it fixed half the problem. I was happy for that. It eventually worked out, as I reported in a separate discussion. Thanks!