My biggest issues with Passkeys is how inconsistently they are implemented and how opaque they attempt to be.
I understand SSH keys, I've been using them for decades, I know where they live, I know how to secure them.
Passkeys are murky as fuck. Is your PW manager supported? Do they sync? Where are they stored? How can I move to another PW manager if I want to in the future? Can I have more than 1 passkey per site? And the list goes on.
I _know_ some of you out there can answer some/all of the questions above but it's mostly on a per-site basis. Passkeys take too much of the control out of my hands and I don't like that.
Even more than that, I hate how they are trying to be pushed on me at every turn. Login -> Want to save a passkey (but they never call it that, they use some other confusing euphemism)? I click "No" and then it proceeds to pop 1Password's UI, then I dismiss that and it opens Chrome's passkey save UI, I dismiss that, and then it opens the OS's passkey UI. It's incredibly disrespectful and unclear.
I never use anything but 1Password but somehow everyone (OS and Browser) try to reach their grubby hands in. This is what scares me, I don't like having to be on high-alert to not accidentally save a passkey in Chrome or Safari and not realize until I'm on a different device and notice it's not in 1Password.
Lastly I trust the developers implementing passkeys... none, I trust them none, zero, zilch. I don't trust them to pick the right defaults, I don't trust their recovery options, and I know they will always pick the configuration that benefits them and not me.
No, for now I'll stick with my as-long-as-you-let-me-make-my-password random passwords which I never copy/paste into random website and be perfectly safe, thank you.