Failure to find X display on TightVNC virtual desktop

Please excuse me if this isn’t the correct place to ask; I can’t find a support forum.
I have a small headless server running Ubuntu 20.04 server. It has a virtual desktop running LXDE accessible via TightVNC.
Nothing installed via Snap runs on the virtual desktop. Examples:

kingqueen@ks3357022:/etc/apt/sources.list.d$ sudo snap install snap-store
snap-store 3.31.1+git187.84b64e0b from Canonical✓ installed
kingqueen@ks3357022:/etc/apt/sources.list.d$ snap-store
Unable to init server: Could not connect: Connection refused
11:53:26:0900 Gtk cannot open display:

Snap Store doesn’t appear in the virtual desktop.

kingqueen@ks3357022:/$ chromium-browser
[65321:65321:0424/] Unable to open X display.

Software with a GUI that I install via apt (without snap redirect) / compiling etc. shows up fine on the virtual desktop.

I have searched and can’t find a way of telling Snap to use the virtual desktop. I’d really appreciate any help or advice anybody could bring please.

Thank you