Something I recently learned from testing the EUS to EUS process, and I like to share the steps here. Starting OpenShift Container Platform (OCP) 4.12, Red hat is adding an additional 6 months of Extended Update Support (EUS) on even-numbered OCP release for the x86_64 architecture.
We can upgrade from a EUS version to the next EUS version with only a single reboot of non-control plane hosts. There are caveats that are listed in the reference section below.
Steps to upgrade from 4.10.x to 4.12 using the EUS-to-EUS upgrade
- Verify that all machine config pools display a status of Up to date and that no machine config pool displays a status of “UPDATING.”

- Set your channel to eus-<4.y+2>

- The channel is set to eus-4.12

- Pause all worker machine pools except for the master machine pool

- Update 4+1 only with Partial cluster update

- Wait for the partial upgrade to complete

- Make sure the partial update is completed

- No reboot for workers as noted that workers are paused on the K8S v 1.23

- Check the OCP console

- Check the KCS https://access.redhat.com/articles/6955381. Review the k8s API version update and ensure the workloads are working properly and will be using the newly updated K8S API version.
- Execute the following command:
oc -n openshift-config patch cm admin-acks --patch '{"data":{"ack-4.11-kube-1.25-api-removals-in-4.12":"true"}}' --type=merge
- OCP console shows

- Click resume all updates
- Double-check all machine pools. If updating, please wait for it to complete.

- Upgrade completed and now showing OCP 4.12 (K8S v1.25)

Reference:
- OpenShift Upgrade: https://docs.openshift.com/container-platform/4.12/updating/updating-cluster-prepare.html
- Prepare for EUS to EUS upgrade: https://docs.openshift.com/container-platform/4.12/updating/preparing-eus-eus-upgrade.html
- Red Hat OpenShift Extended Update Support (EUS): https://access.redhat.com/support/policy/updates/openshift-eus