@klincecum and @tsmith provided the correct code above. Our issue was our FileShare wasn’t correctly pointed to our legacy FTP and a task has been entered for the cloud team to correct it. Thanks to @Epic_Santiago for the assist in getting the bottom of the issue.
Santigo’s Sandbox GitHub code examples is helpful to convert your code
Working Code:
var bartenderPath = new FilePath(ServerFolder.FileShare, "SiteID/bartender/Pilot");
Sandbox.IO.Directory.CreateDirectory(bartenderPath);
var newPath = new FilePath(ServerFolder.FileShare, $@"SiteID/bartender/Pilot/FileName.bt");
Sandbox.IO.File.WriteAllText(newPath, fileData);