Опишите более подробно, что делаете, что хотели и что вышло.

В системе серверный код компилируется под тот же  .net Framework или .net Core компилятором от Microsoft, отличий быть не должно.

Как работать с этим символом, см. тут:

The backslash ("\") character is a special escape character used to indicate other special characters such as new lines (\n), tabs (\t), or quotation marks (\"). If you want to include a backslash character itself, you need two backslashes or use the @ verbatim string: "\\Tasks" or @"\Tasks".

Read the MSDN documentation/C# Specification which discusses the characters that are escaped using the backslash character and the use of the verbatim string literal.

Generally speaking, most C# .NET developers tend to favour using the @ verbatim strings when building file/folder paths since it saves them from having to write double backslashes all the time and they can directly copy/paste the path, so I would suggest that you get in the habit of doing the same.