Some small news, though I don’t know if they have any relevance: I managed to install the Visual C++ 2015 Redist on PlayOnLinux. It required emulating Windows 8.1 and installing dotnet45 (maybe it was obvious, but I didn’t know it), which in turn required setting ptrace_scope to 0.
The bad news are that it improved nothing on launching the Gehn shard, and I can’t replicate the ‘trick’ on MacOS because apparently there is no /proc/sys/kernel/yama/ptrace_scope.
Edit: well, I did manage to install dotnet45 and vcrun2015 (by selecting just those on a new wrapper), but the outcome is the same.