Is there any way to clean up stationary timeline items?

Yep! Definitely. And the good news is once you’ve done the cleanup, new visits to that place will have much less noise/mess in the segments, because the cleanup effort trains the Machine Learning to do a better job at that location.

Basically just go into the Individual Segments view for the visit, and change every airplane/cycling/etc nonsense segment to stationary. It’s a bit of a tedious job if there’s a lot of mess in there, but each time you do it for that place, there’ll be less cleanup work to do in the next visit.

My Home place now gets no nonsense segments at all, most days. Occasionally it’ll get a sprinkle of two or three cycling segments, but that’s much easier to clean up quickly.