As per the latest update of Power BI, there is no such option to format the negative value and to keep the number data type at the same time. However, you can create a calculated column to return the format. But in this case, the result will be treated as TEXT instead of a number.
Column = IF('Table2'[Column1]<0,"(" & FORMAT('Table2'[Column1],"General Number") & ")" ,FORMAT('Table2'[Column1],"General Number"))
Hope This Helps!!