Try  Multipart3D.com
 

Multipart3D is a free browser tool to split STL and painted 3MF models into printable parts.

As you might also experience: slicer cutting is very limited. Slicers aren't designed for altering 3D models. CAD is overkill for a simple split. Multipart3D sits in between.

What it can do:

- Simple planar cuts, specific area cuts, and dovetails
- Smart detach
- Separate by color on painted 3MF
- Several types of connectors: dowels, magnets, snap-fit, pin holes, and more
- No account, no upload, files stay on your device

This listing is a demo model. The tool is not something you'll open every day. Handy to keep bookmarked for oversized models, better orientation, assemblies, and multi-color splits.