The guidelines I follow for C# has "use var where it's obvious, but explicitly type when not".

So for example I'd write:

  var x = new List<Foo>();

Because writing:

  List<Foo> x = new List<Foo>();

Feels very redundant

Whereas I'd write:

  List<Foo> x = FooBarService.GetMyThings();

Because it's not obvious what the type is otherwise ( Some IDEs will overlay hint the type there though ).

Although with newer language features you can also write:

  List<Foo> x = new();

Which is even better.