This folder contains an updated binary
The NuGet package of Mono.Posix and Mono.Unix contains a library for 32-bit Arm that is built without large file support.
This causes it to fail when processing files that are larger than the 32bit values (i.e., 4 GiB).
The binary in this folder is built from the Mono.Posix source on Ubuntu, which default enables large file support for Arm cross-compiles.
The issue is reported to Mono.Posix and this folder should be deleted once upstream is fixed, but at this point the package has not been updated in 3 years, so it is unclear if an update will ever happen.