DNS not working inside Ubuntu VM (running docker)

I have a VM managed by Proxmox that's running Ubuntu 20.04 (desktop) and is also running docker (with portainer). I can't get any dns resolution i.e. if I do ping google.com it says Temporary failure in name resolution (if I ping 8.8.8.8 it's fine). However, if I do it in another VM that has identical OS and Proxmox settings, it pings fine.

In both VMs the /etc/resolv.conf file is identical; it just has the two lines (as well as a huge comment saying not to edit this file because it's managed dynamically):

The Proxmox node itself has two DNS IPs set; 8.8.8.8 and 8.8.4.4. Seems absurd that installing docker on one VM should nuke the DNS...