it is
best I can figure is you use FC with one of the gazillion options it has that gets you kind of close to diff-like and then do some extra leg work on Windows
or write one (which is admittedly a decent sized job)
I’m sure you already read
https://stackoverflow.com/questions/6877238/what-is-the-windows-equivalent-of-the-diff-command
which asks almost this exact question
part way through one fellow points out that you can get fc to be “sort of diff-like” but that it wont be the same as diff
it seems even on that thread the conclusion is there is nothing built in