I missed the part that Incus supports clustering, for some reason I thought it's single node only.
I'm not sure that clustering goes beyond "multiple hosts with single API to rule them all" - thus I assume when physical node needs maintenance, it won't magically migrate / restart VEs on other cluster members. May be wrong here.
P.S. Microcloud tries to achieve this AFAIR, but it's from Canonical, so on LXD.
To some extent, of course things like vSphere/Virtuozzo and even LXD/Incus, and even simple Qemu/Virsh systems can do live migration of VMs, so you may care less on preparing things inside VMs to be fault taulerant, but to some extent.
I.e. if your team do run PostgreSQL, your run it in cluster with Patroni and VIPs and all that lovely industry standard magic and tell dev teams to use that VIP as entry point (in reality things bit more complicated with Haproxy/Pgbouncer on top, but enough to express the idea).