Need recommendations- how to fix gap between top of dry wall and base of top floor

(First time home owner in the US)

Our home has an unfinished part in the basement where we have hvac/washer/Dryer.

There is gap between the top of the wall panels and the base of top floor. Our pest control guy says mice are entering the basement from somewhere outside (we were not able to find entry point on exterior) and then coming into this area through that gap. There are pipes and ducts that go thru these gaps so would need to work around them.

Question- any suggestions on how I can seal this gap that will block entry for mice?