I've already figured out the answer, but decided to post this as a Q+A here because this bothered me for ages and it took a long time to find the solution.
Hoping this will be of use to others (or even myself) in future...
Unable to browse network with Thunar.
OS: Debian XFCE (minimal network install)
Issue: Open Thunar and click "Network" -> error appears stating that operation is not supported
The issue is that the minimal/network Debian install comes with exactly that - minimal packages.
In particular it is missing any support for Samba.
For browsing to work in Thunar:
sudo apt install gvfs-backends gvfs-bin
You may also require some or all of these packages:
sudo apt install smbclient samba
Additional note: My samba share is hosted on a TrueNAS instance. I needed to go to:
Network -> Global Configuration -> Enable "NetBIOS-NS"