”But even with Apple, I can't sync stuff between my personal and work computer because they use different Apple IDs, even though the underlying true identity (me) is the same.”
Apple has recently addressed this. You can now create shared groups, and selectively assign passwords and passkeys to the groups. You could easily create a group with your two identities and move the credentials to that group.
https://support.apple.com/guide/iphone/share-passwords-iphe6...