silly me - evaluate is Shift-Enter, which works fine.
so tightvnc is fine too, probably more lightweight if you don't want the full desktop.

some observations: 1. see tightvnc docs to set password, and start tightvncserver before it allows connection 2. tightvnc default settings don't seem to have a US-keyboard, so Ctrl-Enter (to evaluate) does something weird -- but definitely works because menu "Evaluate" works fine 3. just tried xrdp ...

Thank you. Uninstalled vnc4server, installed tightvncserver, works!!

removed xrdp, installed vnc4server instead --
https://linuxconfig.org/quick-vnc-serve ... x-jessie-8

same problem - as mathematica starts the connection aborts