Hello a123qwertz567, if there are no way barriers, I guess there is nothing that we can really map. I also found no official map where the exact outlines of the military area are shown. So maybe this is only a sign to warn people that there could be old military stuff lying around but it is no "real" restricted area and everybody can walk here. I would close this note for now.
We have another note in the same area with a slightly different but similar topic: https://www.openstreetmap.org/note/2975688
After the flood 2021, a lot of ways are blocked. I would combine your note in this other note and if we find something more that we can add to the map, I would add it there and remember your information.