PART 1
The problem applies equally everywhere and is becoming increasingly annoying, as the general driving bans are completely meaningless, since they actually prevent motor vehicles from driving over corresponding paths (especially in the forest, although there are actually no prohibition signs required for this, since a general driving ban for motor vehicles in the forest applies) should deny. This then leads to the ugly situation that - theoretically - bicycles would also be included.
The fact is that the signs, as rightly mentioned, were installed a long time ago. Whether all of them were sanctioned by means of an application / permit / published and thus - if without objection(s) - I doubt it!
At that time there were still very few bikers (in the forest) on the road. This has changed significantly in the meantime and so many (especially those who are not on bikes) believe that everything is right, cyclists have nothing to do in the forest and therefore mostly on "hiking trails" (I mean explicitly on the Forest paths / forest roads, trails are a completely different story and off the beaten path, i.e. in open terrain, we don't have to discuss that anyway! True to the motto, it's called hiking trails, so people hike there and don't drive).
Well, you can be very wrong, but according to the current legal situation, that is absolutely NOT the case! Only motor vehicles are strictly prohibited from entering the forest. On the contrary, RIDING and CYCLING in the forest is explicitly allowed!
This in turn means that the general driving bans are often illegal and would have to be replaced by three-part prohibition signs (motor vehicles, motorcycles and mopeds > this also includes fast e-bikes, just a reminder!) because the justification for maintaining them A general driving ban does not exist in the majority of cases, then as now.
Why is nothing changing? Because nobody wants to take legal action and no forest owner, municipality or anyone else will voluntarily update (or even better > dismantle) the signs, as this involves considerable costs and you are on the right / good side anyway believes. Thus, many bikers are criminalized, although completely unjustly, simply because of the inaction of those responsible.