Proxmox

The ultimate hypervisor.

This is the ultimate secret ball knowledge I have acquired from the goat Christian Lempa in this video.

Proxmox Certificate Fetching using ACME

Navigate to the ACME menu in your Proxmox management web UI. (Datacenter > ACME)
Connect your account with your DNS provider. This example will use Cloudflare.
Which means I have to head to the Cloudflare Domain Dashboard again and generate another API token.
Use the "Let's Encrypt v2" or "... v2 Staging" (for getting untrusted certificates that are only used for testing purposes)