I'd think German traffic engineers could come up with a better solution, yet these are everywhere:

The bike paths themselves are desire paths for cars and motorcycles.
To block them off, they put up barriers, but those also block cargo bikes, wheelchairs and strollers, create a collision hazard, and force all cyclists to stop and dismount for no reason.
Of course, they'll be bypassed wherever possible – naturally by cars and motorcycles too, if there's enough room.

Side on view of said pictures ?

They get used in parks here with plenty of room from the front and back post as they are staggered. But here they’re used to stop kids on motorbikes, quads and skidoos.

Yes, they're staggered. You can walk your bike through, but not safely keep riding.
And they're close enough (<1m) to make it really difficult with a wheelchair, cargo bike, loaded panniers or modern MTBs with their broomstick handlebars.

On the first one even cars could fit on the side

These are worldwide, they keep motorized vehicles off paths except for maintenance.

You ignored the side view, they can be easily traversed while on bike, I do it every day. But I love when the Internet second guesses engineers. Guess why these are on either side of a public road? Because otherwise idiot cyclists would not slow down and get hit riding into live traffic.

The point is to not have people riding onto the road.

I'm aware of their function. But they actively make the bike path worse for all users and block it off for some legitimate uses (wheelchairs, cargo bikes), that's why I'm saying there has to be a better solution. Like putting up blocking posts with a distance of ~1.8m on both sides of the path would be enough to keep cars from entering.

And if there's so little traffic on the road that cyclists don't expect it and slow down naturally, it might be a good idea to give cyclists the right of way at that intersection and design it accordingly.

I'm aware.
It's to force cyclists to dismount (which by the way isn't possible for all vehicles allowed on that path), instead of forcing cars to stop by changing the right of way.

The people who plan this bullshit grew up in a time whether there were only granny bikes. Actually, sometimes I think all traffic planning in Germany is being done by drunk chimpanzees.

So it's okay if that means disabled people can't use the park?

This particular design is more aggressive than simple bollards for sure, but in general I file these devices under necessary evils. The real solution oftentimes is getting usage of a path high enough that social pressure is an effective deterrent, but that's a longer-term system level goal.

Cyclists seriously aren't a hazard, unless they're fat bikes. And this blocks wheelchair users.

Stop and dismount? Those seem completely navigable mounted imho. Why would you dismount?

Gate Gate Paragate Parasamgate Bodhi Svaha !

Unless the bike has a trailer, or it's a cargo bike, sometimes even mobility scooters may struggle.

Good luck getting a kayak through too, one of these means I need to take a pretty big detour when I want to go kayaking.

IF you have a small bike maybe. I often have a kid on trail-a-bike. Sometimes I have a second kid in the trailer behind that. The train cannot be got through that. Even my road bike alone often cannot make those tight turns without dismounting, but it depends on the exact geometry of the gates.

Are the gates hinged so they can move back and forth, or are they stationary? If they are stationary they need some "saloon door" style hinges so they can swing back and forth, but default to the middle, blocking the path.

Also what do those blue signs mean?

Hinges: some do, but they are typically locked with a key. The easiest would be bollards ("poller")

Blue sign means: pedestrians and bikes have to use this, and they share the path. If the line would be vertical, it would mean bikes/pedestrians have their own lanes

Thanks!

They're stationary. The blue signs mean it's a combined bicycle and footpath.
They imply: banned for all motor vehicles, and if they're parallel to a road, bicycles must use them and not the road.

Thanks!

Those look annoying. Here they use bollards with a collapsible one on the centre so you can easily walk/bike through the gaps but maintenance vehicles can still get through with a key. Guess they don't prevent motorcycles but neither do the gate style in the OP.

I don't understand why they don't just use 2 posts 1.8m apart on either side of the bike path.
It would be much safer and more convenient for cyclists and still keep cars out.

Motorcycles usually aren't an issue on these paths, except for the occasional old guy or youth on a 50cc, and there's nothing that keeps them out and lets cyclists through.
The bigger bikes want to go faster than is possible on those paths.

youth on a 50cc, and there's nothing that keeps them out and lets cyclists through

noise activated land mines!

Or even worse these things where I almost don't fit with a stroller and which are dangerous for kids because they try to bike through without dismounting:

Luckily my town removed all of them recently.

At least for the dams I can answer that. The posts, if removed, are a hazard when there is a flood. You’d need extra man power/time to collect excess posts in a moment when these factors are critical in fighting against flooding. Yes, it’s not the standard to drive atop the dam, but before starting to fortify it there needs to be a measurement of how well it’s doing where.

I'd be concerned about just not seeing the chains until it's too late.

Still better than these abominations I saw on the official long-distance cycle routes in the UK a few years ago. Was a lot of fun unmounting all my luggage every time. And good luck with a stroller or a wheelchair.

Btw. your second picture shows, how these things are meant to be installed. ~1.5m apart, so you can easily drive around them, even when going 30kph or with a cargo bike, but not with a car.

Huh. I wonder... could you create an EMP mine powerful enough to fry the electrical system of a car or motorcycle? Interesting idea.

Please don't underestimate drunk chimpanzees. They can use and invent tools!

Oh, I don't. They're very good at always finding the worst possible solution.

I had a friend hit that kind of chain at full speed on his bike. He was following me, I went around, and he never knew why until it was too late.

He was hurt pretty bad.