I never put my 3 Proxmox boxes in a cluster because some of my VMs can't run on other boxes: OPNSense requires the PCI 4 port card and Home Assistant has two USB dongles.
I also didn't want to worry about the quorum thing which can cause issues.
I debate putting them in a cluster every once in a while but just leave them as is.
I can somewhat easily move VMs around by restoring a backup that lives on the NAS, so that's good enough for now.