Exterior wall plugs?

If this hole is in a stud bay in your wall then you're likely looking at 1/2 inch OSB or plywood. If so then you need a 4 inch plywood disc. In order to secure it in place you should get a piece of plywood that's about 1.5"x6", place it behind the exterior wall, and fasten it to the wall with a screw on each side. Once this cross-brace is in place then screw your 4 inch disc to the brace.

If this is through your rim joist then you'll need a 4 inch disc that's as thick as your rim joist. You should be able to put the disc in the hole and secure it with wood glue if it's snug or epoxy if there are gaps. You could also choose to support it with a cross-brace from inside your home similar to the plywood method.

If you have no idea what I am talking about then this image should help:

Courtesy of https://www.dreamgreendiy.com/2019/01/21/how-to-patch-a-hole-in-drywall/