Prepare the plot

no, ... by the way, congratulations and I’m glad that you will support us now

Vandalism remains vandalism... whether it is perceived as disturbing or the boundary distances were not observed. It is still property that you cannot simply clear without permission.
The neighboring law also has no influence on the Criminal Code.
Certainly, neighboring law applies in most cases, but not regarding property and so-called vigilante justice over the garden fence

P.s. we are not talking about windfall fruit or other little fruits

Thanks for the compliments, but you are wrong. This is not supposed to be legal advice, but just google "Kapprecht" and §910 Baugesetzbuch.

However, it remains (quite consistently) with § 910 of the Building Code in the previous request with a reasonable deadline for the offender. If they do not arrange for the removal of the disturbance, then according to § 910 of the Building Code, "cutting off" is permitted. In this respect, you are very close.

Simply clipping off someone else's property does not exist in Germany (fortunately) and would generally contribute little to neighborly peace.

TE asks if he can just do that. And then § 303 StGB applies. I do not need legal advice, I belong to the law enforcement!