pashley APB became the Moulton TSR so back to the original question.
<span style=”font-size: 0.8rem;”>The point is that the Moulton is designed with suitable clearances and wayyy back in the day, was a viable mountain/rough stuff bike. If I recall correctly you can fit 1.6inch tyres with mudguards or 2inch without.</span>
I’ve only ridden one offroad once or twice and I would go for almost anything other than small wheels.
I wonder how important the folding is to the OP. I have a bike for trains, busses, taxis and the like. For this a brompton was the only choice as folding trumps all. I’ve ridden it on forest tracks in the dry and it’s ok. Better than not riding. Given you’re looking at moultons and other collapsible rather than folding bikes, have you looked at something like:
https://ritcheylogic.com/break-away-ascent-frameset