A lot depends on what is around you. I see photos and have watched videos of cyclist on nice trails through pastures and woods in the UK and this is far from what is around my house within an hour drive time. What I have are technical trails which require a mountain bike of some sort.
Folding bikes are heavy and not something I would want to pull out of a car trunk. There is a couple that have traveled for years with their folding bikes and will fly into a city and then use the bikes by themselves or put them on a bus or train as part of their trip. I can see a lot of value in their approach. If I lived in Europe it would be a no-brainer.
An intermediate bike can be created by adding a dropper post to a gravel bike. I did this and total cost for the post and lever and labor was under $400. Being able to lower the seat out of the way made my stability a good deal better on rough surfaces.