Answer by Parfait for Remmina VNC Hangs on Connecting to Headless Mini-PC

Eventually, I found my answer: no vncserver was installed on the mini-PC (facepalm) and possibly why the Connecting... dialog simply hung waiting for a VNC session.

Simply I did the following:

1. Installed tightvncserver, created vncserver password, and adjusted the startup file.

   $ sudo apt install xfce4 xfce4-goodies tightvncserver$ mv ~/.vnc/xstartup ~/.vnc/xstartup.bak$ gedit ~/.vnc/xstartup$ sudo chmod +x ~/.vnc/xstartup

2. Then in ssh, started the vncserver on mini-PC.

   $ vncserver

3. Finally, on laptop client, I opened the port.

   $ ssh -L 5901:127.0.0.1:5901 -N -f -l username server_ip_address

   And then with Remmina I logged in connecting to localhost:5901 entering the ssh password (for tunnel) and vncserver password created above in step #1.