I store my passkeys in KeePassXC and I have absolutely no feeling of being walled into any garden, personally.
I believe that by allowing password managers to store passkeys, the whole purpose of "device based security" got lost..
And yes, I know the happy path of password managers uses host-based autofill which does add some friction to phishing attempts, but given the prevalence of unexpected but legitimate urls with weird alternate subdomains/SSO/redirects in modern login flows, you have to manually autofill/add an exception often enough that it's possible to let your guard down once at the wrong time.
UPD: oh, heck, attested passkeys are actually already in the protocol. Why can't we just have nice things?