Thank you for all those pointers, Laurie and Magnus.

So, I pretty much set up my scene by pretty much removing all shaders and leaving only colourMaps and bumpMaps. No connections anywhere to Alt_anything. Took out the building, simplified to BB water shader to just a colour, and had the poor girl stand nude in the water wondering what had become of her dress. So: Charlotte / Koz's bob, clothPlane with colour and skyDome. 3 lights: IBL, pointlight (sun) and specular light.

In Pose2Lux, went with 'analyse scene', and assigned default materials. The sun was the pointlight, the sky was IBL. Left other values to whatever the default was.

Brought up LuxRender, which, to my surprise, started rendering immediately after I chose the scene. The output was rubbish. So, no makeArt button here either. As in good-ol' time-honoured tradition, tried to go with defaults and created rubbish.

Time to hit the books.

Monterey/Mint21.x/Win10 - Blender3.x - PP11.3(cm) - Musescore3.6.2

Wir sind gewohnt, daß die Menschen verhöhnen was sie nicht verstehen
[it is clear that humans have contempt for that which they do not understand] 

Metaphor of Chooks