The OpenKeyChain is unrelated, as that’s for pgp and keepass just needs an HMAC. I was curious and tried KeepassDX. Its help suggests to install its keydriver app, which still is missing Nitrokey support. However, it did not work with a yubikey for me either. I just tried to setup a fresh db and it never completes database setup, despite recognising the yubikey (which already fails for the NK3).