Tubesync is pretty great

Not if you’re serving content to a device that can do the decoding, like a Shield. My Jellyfin server runs in a Proxmox VM with no GPU passed though, and transcoding disabled for all accounts.

If you’re rural, check out B4RN.

Unfortunately not, it applies to all clusters. A quorum requires at least 2 votes, which means 2 nodes. But if one node goes down, you only have 1 vote, and the cluster will go into read-only mode, which means you’ll lose the GUI and the ability to manage your nodes:

When your cluster is non-quorate (so at least half of all nodes are dead), the remaining nodes will change the PVE management into read-only mode. Because of that you will no longer be able to change and manage your VMs and containers and will also not be able to log into the GUI. This is done to avoid cluster split-brain problems in which they run into inconsistent states. (Source)

But if you have a device that will supply a vote in the event that one of the two votes is unavailable, the cluster will continue to function with a single node, which will allow you to use the normal Proxmox tools and interfaces to diagnose the problem, while also keeping any VMs on the single remaining node up and running (available).

Here is a Proxmox employee explaining it a bit more clearly than the official documentation:

… a cluster needs to be always quorate to work properly, not just for HA. High availability just means that the cluster will try to keep your HA-enabled VMs and containers always available, i.e. if a cluster node fails the HA-manager will launch HA-managed guests on another cluster node.

While a 2 node cluster should work with 2 active nodes, if one of your nodes goes down your cluster will automatically be non-quorate and will no longer work as expected. To have quorum in your cluster, you need a setup of at least 3 nodes, though you do not need 3 full Proxmox installations … you can setup something like a Raspberry Pi as a QDevice for external vote support.

(Source)

You may have trouble keeping a quorum with a proxmox cluster of 2. You should really have 3, or set up a q-device. (Source)

Each node in a cluster has a “vote” in a healthy cluster. If one of your devices goes (or is taken) down, you’ll lose quorum, and the GUI and some other stuff. You need 3 votes for things to work reliably. I have an old RPi set up as a q-device and it works fine.