https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/17.1/html-single/framework_for_upgrades_16.2_to_17.1/index#proc_updating-the-default-machine-type-for-hosts-after-upgrade-RHOSP17_post-upgrade

Section 11.3. Updating the default machine type for hosts after an upgrade to RHOSP 17

We need an optional step to update image properties, in case the instance is using hardware that no longer exists with the Q35 machine type, ex: the IDE disk bus. In such cases, image properties need to be updated using the nova-manage image properties update commands.