Is this still an issue? Others don't seem to have this problem.
Eduard Metzger: Yes. JS Console: "Failed to load resource: The certificate for this server is invalid. You might be connecting to a server that is pretending to be “api.apple-cloudkit.com” which could put your confidential information at risk". Is there a setting in the preferences I'm missing?
Aristostat: Not sure, I haven't changed anything, I found a radar for this filed for Apple: https://openradar.appspot.com/43295319 Sounds like a Safari or CloudKit issue, I'm just loading their library from the link which was provided by Apple. I suppose you tried the whole restart your complete machine routine and maybe re-install Safari?
Eduard Metzger: Yes. I've restarted and even updated MacOS since first running into this. Issue is consistent. Again, shared notes display fine on iOS Safari, Brave browser, etc. I'll continue to look into it on my end.
Receive warning when attempting to visit webpage
Console warning: certificate invalid
It turns out it was the iCloud private relay. In the preferences, under Security, is the option to hide your IP address from trackers and websites. Deselecting this option in Safari MacOS allowed for the shared notes to display. Reselecting it had no effect (so far) on newly shared notes.