[openstack-ansible] Compute nodes with mixed system releases

Hello, I can ot find a real answer in the OpenStack-Ansible docs. Can I add Ubuntu 18.04 compute nodes to my actueal all Ubuntu 16.04 cluster ? Ubuntu 18.04 needs Rocky, so I will first migrate from Queens to Rocky. But then, do I need to stick to 16.04 and plan an overall upgrade after ? Of course, I understand that mixing Ubuntu release, will also mix kernel and qemu versions and can pose problems, for migrations for example.