Reference:
https://www.blackbox.be/en-be/page/27559/Resources/Technical-Resources/Black-Box-Explains/kvm/ Benefits-of-using-KVM-over-IP

The best practice for troubleshooting is to follow a logical and systematic process that involves identifying the problem, establishing a theory of probable cause, testing the theory, establishing a plan of action, implementing the solution, verifying functionality, and documenting findings. Since the problem occurred after a change in the server's BIOS, the most likely cause is that the change was incompatible or incorrect for the OS. Therefore, the next step should be to reverse the latest change made to the server and reboot to see if that fixes the issue. Reference: https://www.comptia.org/training/resources/exam-objectives/comptia-server-sk0-005-exam-objectives (Objective 4.3)

Explanation
This is the best action to perform before applying patches to one of the hosts in a high availability cluster. A high availability cluster is a group of hosts that act like a single system and provide continuous uptime. A high availability cluster is often used for load balancing, backup, and failover purposes. Failover is a process of transferring workloads from one host to another in case of a failure or maintenance. By failing over all VMs (Virtual Machines) from the host that needs to be patched to another host in the cluster, the technician can ensure that there is no downtime or data loss during the patching process. Disabling the heartbeat network is not a good action to perform, as this would disrupt the communication and synchronization between the hosts in the cluster. Fallback cluster services is not a valid term, but it may refer to restoring cluster services after a failover, which is not relevant before applying patches. Setting the cluster to active-active is not a good action to perform, as this would increase the load on both hosts and reduce redundancy. References:
https://www.howtogeek.com/190014/virtualization-basics-understanding-techniques-and-fundamentals/
https://www.howtogeek.com/428483/what-is-end-to-end-encryption-and-why-does-it-matter/