I found a working solution for my needs: filter_poi(las.norm, Z > 1 & Z < (max(Z) - 3))

This code filters the point cloud to display only those values between 1m from ground level and 3m below the highest point, as I was looking for.

I'm sure there are other answers, such as the solution proposed by @Chris in his second comment, but this one feels simpler for me.