I might have found a bug in Proxmox, but I somehow doubt I'm the first person to stumble upon it.
TLDR: Proxmox generates a self-signed certificate that I want my laptop to trust, but it looks like the CA cert is missing a crucial key usage extension.
Have you already stumbled upon it? Am I holding it wrong?
https://forum.proxmox.com/threads/the-root-ca-seems-doesnt-contain-the-key-usage-extension.169961/