The term is often used without a clear definition. As a passkey should be used instead of a password, it means that you need "user verification" (PIN or biometrics) to protect the access when the device is lost.
The other thing is that it is more convenient to have "discoverable credentials" (a.k.a. "resident keys") so the browser can check if there are passkeys stored on your FIDO2-authenticator for a specific website. (instead of asking for a username first)
Syncing is optional but if your passkey is not synced, it is usually called a "device-bound passkey" (e.g. Windows Hello).
Thanks for the link - I signed up for a free 2 GB Nextcloud with one of their partners. Experimenting with non-iCloud hosted notes now. It's a bumpy ride, lots of room for improvement.
I've seen that map before. Re-checked it now. It's hopelessly outdated/incomplete. My few thoughts about that at the times were: What about all the cameras in shops? In public transportation and stations?
Now there are even more cameras, for instance on top of the traffic lights of streets where buses drive.
What is the goal of that map? What would be the goal if it were complete? Should I protest? Slingshot/Laserpoint them? Making detours around them? What if a cluster of them popped up near a literal hotspot where some assholes set cars and market stands on fire?
Both use-cases (VPS and homeserver) are valid. As FreedomBox is just a bunch of Debian packages it should be easy to offer it as a base image (or 'apt install freedombox' it yourself).