If the gap is too large to caulk and your wall isn’t wavy against a straight edge, then you could use a color-matched piece of scribe molding. You’d probably want to use a nail gun, but more or less just make sure it will fit against the wall with enough room on the cabinet stile to attach (but not so wide that it hits the hinges). Once you’re ready to add the piece, cut it to length, run a line of glue where it will contact, then hold it snug against the wall and put a couple of brad/pin nails through it into the cabinet behind. Putty+touchup paint would be a good idea if you go this route.

If the wall isn’t straight then it might need to be cut to profile, which is more complicated but doable. You’d essentially need to make a proper scribe cut which may require a pencil and a saw. Of course, you could skip this and just apply the molding in combination with a very thin caulk line and then likely wouldn’t be able to tell it’s uneven (again, as long as the wall is reasonably straight)

Most hardware stores carry pre-finished scribe molding, and I’d highly recommend taking a door off its hinges to compare with the color selections available in store. Hell, if you pre-measure the exact width and length you need the molding to be ahead of time, many stores offer a service to get it pre-cut to size which helps things go as smoothly as possible. This is assuming you don’t have the tools on hand of course.

All that said, if you can fill the gap with a single bead of caulk running down the length, that’s almost guaranteed to be your best bet. Either way, you will almost certainly want to clean up the existing foam first.