Garden fence: on which side are the fence posts?

If the neighbor on the left wants to put up a hedge anyway, the acceptable version would be that the mat and thus the nice side faces you. One has advantages that do not harm the others.

Advantage: If the neighbors ever sell the house, it gives the impression that the fence belongs to us, since the fence posts are on our side.
Then we don’t have to forcibly prove that we paid 50% of the fence back then,

If the new owner wants to push it, then one would have to prove that we contributed 50% to the fence if the posts are on their half

Who has to prove what and why, you will see when there is a dispute about the fence. Even torn-off sections of the plastic privacy screen alone could cause trouble, but also the maintenance. Besides, you don’t know who will move out first…
I would anyway draft a short 3-liner in the sense of a community agreement—exactly because of such petty thoughts that it might belong to him/me.

We have now decided that the fence posts will be on our side on both sides, so in the future it will definitely look like we built the fence and later on (if it even happens) we will not be obliged to provide proof.

We definitely wanted the fence because we have a dog who could escape through the hedge.

We also wanted the privacy screen as wind and visual protection.

We are glad that the neighbors contributed and agreed to it.

then it definitely looks in the future as if we built the fence and later (if it ever happens) we are not obliged to provide proof

Oh how naive. Do you really believe that in 10 years anyone will care about how it was built?
If someone is looking for a dispute, you are still obliged to provide proof. And if it partly stands on someone else's land, trouble is guaranteed.
Just place it 5m further to your side. Then it is definitely yours too.

Though 5 cm are surely enough as well... ;D

Isn't it the case that with a boundary construction, the fence automatically belongs to both parties? And if no boundary construction is made, at least 50cm distance from the boundary must be maintained?

Isn't it the case that with a boundary construction the fence automatically belongs to both parties? And if no boundary construction is done, at least 50cm distance to the boundary must be maintained?

Both no, at least not so generally.

Yes, an enclosure can be placed right on (!) the boundary but for example the classic double rod panel fence is turned into a wall by weaving these plastic strips through the fence and is then completely impermissible.