You're right, I could enable OpenGL from raspi-config. Testing it directly with a monitor it now works - however I still have a problem with XRDP which is the main use case anyway as I'll be operating on it remotely. I haven't found a solution for this yet. But yeah, this is a non-Ekos problem... I wonder if anyone else has run into this before.
Oddly enough, glxgears does run just fine under XRDP. When starting KStars however I'm getting the errors:
QXcbConnection: Failed to initialize XRandr
libEGL warning: DRI2: failed to create any config
And then when it crashes:
Xlib: extension "XInputExtension" missing on display ":10.0"
And in the kstars log file:
[2018-08-19T14:24:49.942 EEST WARN ][ default] - QXcbIntegration: Cannot create platform OpenGL context, neither GLX nor EGL are enabled
[2018-08-19T14:24:49.943 EEST FATL ][ default] - Failed to create OpenGL context for format QSurfaceFormat(version 2.0, options QFlags(), depthBufferSize 24, redBufferSize -1, greenBufferSize -1, blueBufferSize -1, alphaBufferSize -1, stencilBufferSize 8, samples -1, swapBehavior 2, swapInterval 1, profile 0)
So, definitely OpenGL and XRDP related issue. Now I just need to scour the internet to find a fix...