If the path actually exists, regardless if it's overgrown it should stay on the map, perhaps tagged with `overgrown=yes` or `trail_visibility=...`. I'm completely fine with that. I've just removed it then cause I just didn't see it at all, it just seem to end for me from the point I've removed it.

Some side notes: looking at Geoportal the land plot that's owned by PZM (I assume) starts about 13m from the river, so any path in that area is almost certainly public.

> this path near PZM near Brda River is the only legal option to go through because it's forbidden to go by PZM's tracks.

well, not entirely, since the land is not entirely surrounded by fence you  legally can go there and stay until someone tells you to go away (https://repozytorium.kul.pl/server/api/core/bitstreams/40364972-b5aa-47f6-8474-f6a5bb4b647a/content)