Except when the ONLY pi-hole is down, which was the original OP’s whole question.
Except when the ONLY pi-hole is down, which was the original OP’s whole question.
Yes, your experience will be different if your DNS is being provided by another kind of DNS resolver. If you want a consistent pi-hole experience (and you can’t avoid downtime of your current pi-hole), add another pi-hole to your network and let that be your secondary DNS resolver.
Add another DNS server (1.1.1.1, for instance) to your DHCP options. Your DHCP clients will use 1.1.1.1 when the pi-hole isn’t responsive.
VLANs all the way. I have several VLANs, including:
EDIT: An alternative would be to replace or supplement Proxmox with Docker/Podman on the bare metal of the server. The container networking would be isolated by default. If you can replace your VM needs with containers, that may get you what you want.
Per rule #3, this seems to be a general home computing question and not centered around self-hosting. Please consider adding details to clarify how this involves self-hosting.