Windows long path as current directory

Question

If I understand this doc correctly: https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation?tabs=cmd all calls should work with long path. I have Windows 10 version 1909 and the registry key Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem\LongPathsEnabled set to 1, I am unable to start a process in a long path:

In C#

using var process = new Process();
var processInfo = new ProcessStartInfo
{
    WorkingDirectory = "C:\\Long\\Path", // Or "\\\\?\\C:\\Long\\Path"
    FileName = "powershell",
};
process.StartInfo = processInfo;

process.Start();

Or in java

ProcessBuilder pb = new ProcessBuilder("cmd", "/c", "start", "powershell");
pb.directory("C:\\Long\\Path");
Process myProcess = pb.start();

I end up having an IOException: 'The directory name is invalid'

Also, git doesn't work when the current directory is the long path: I see a new console for half a sec. But all file manipulations are working fine (create, move, copy, delete)

Am I doing something wrong? Am I missing the doc section about the current directory? Is it a bug / missing feature?