KeepassXC seems to have included that for two years now: https://github.com/keepassxreboot/keepassxc/pull/8825 (I don't use Keepass, so I can't attest to how well it works.)

There's a JSON example of an export on the page. It shows nicely what's stored on your machine.

It's a non-standardized format, because a standard is still being worked on. I think most vendors are just waiting for that. The FIDO Alliance has a news message about it: https://fidoalliance.org/fido-alliance-publishes-new-specifi...

In the article they mention they are not just going to support exporting passkeys, but also passwords and other credentials. The goal is to create a secure exchange format for that. They have published drafts of the standards.

It is that trivial. The problem is vendor lock-in and no common, defined way to export/import them securely (which is going to change soon).