I think it will be hard to do. The reason is that to export to Keepass you will need to decrypt the secrets from the Passbolt database before creating a Keepass database file.
But, the thing is that in the Passbolt’s database the secret are encrypted for the users who have access to the secrets with their own public keys. Thus, to decrypt the secrets you will need the user’s private keys to proceed, which you normally don’t have and would brake the security IMO.
However, what I understand from your message is that you could go with a backup on your Passbolt instance. If so, yes, you can do stuffs with cli.
Here’s a help page to proceed with backup if you wish