Trim brush goes haywire

When watching Nomad videos on Youtube, I often see the trim brush being used. However, when I try it, I often get a messed up mesh. Nomad seems to randomly flip the normals of the surface. Here I added 8 cylinders using radial symmetry. Then I did a voxel remesh. And finally I did a rectangular trim in front view in order to clean the uneven surface. Tried the project brush as well, but this gave even crazier results.

It gets even worse, when less polygons are involved. This is a lowpoly plane. I saw several videos, where a such a plane was cut in shape an then extruded. Here’s the only result I ever get:

Am I doing something wrong?

Most likely you’re doing something wrong, yes.

On the plane, it looks like you have Fill Holes enabled. So after cutting it, it then filled all the holes (aka makes it solid) so that’s why the mesh is like that. Uncheck Fill Holes and it’ll solve it.

The cylinders, I’m not sure. Trying to think of what it would be.

For the plane: disable Fill holes in Trim settings.

For the cylinder: trim with Fill holes disabled and you’ll understand why it struggles to fill the thing.
One solution is to voxel remesh first to remove the inside intersection of the cylinders.

Also, remember that the radial settings also apply to the Trim tool, for the cylinder scenario it’s probably best to disable it.

Thanks for the solution. Disabling Fill Holes did the trick. I just realized, that I did not do a voxel remesh before trimming the cylinders. The topology clearly shows this. My bad.