Neighbor's tree - Security and dirt. Who is responsible?

At a height of 2.5 m, hardly.

The trees have been overgrown with ivy for years, which will soon completely kill the trees - not much is missing; hence also the many dry branches.

It may also be necessary for the municipality to intervene if there is an imminent danger; which is indeed the case with dead/half-dead tall trees. Have you ever contacted the Ordnungsamt?

Stealing the nutrients from the ivy is enough. Just remove 5cm near the base of the trunk and that's it. By the way, it doesn't even look good over a longer period.

I wouldn't - if the trees are obviously dead, then you have a better chance that they have to be removed.

If the trees are really dead, it is of course too late, you are right.

Am I the only one who sees massive double wire mesh fences with fully opaque plastic crap? Accusatory pictures of pinecones and a thread title with an exclamation mark, "Security, dirt, and responsibility." It doesn't seem particularly social to me. I don't need much imagination to put myself in the situation of the neighbor who has had his conifers standing there for decades. Maybe I am just overly sensitive.