Quick and dirty 5 minutes craft: Draw a rough shape, define the contact surfaces & load, click run, and get the optimized shape. The last step is converting the output to a printable shape and running one more simulation to double-check it is strong enough.
This particular holder is a filament spool holder designed to be loaded with up to 5.5kg of filament (1x2.5kg, 3x1kg).
The thing with 3D printing is that it is usually stronger and uses less filament when you do a full shape without holes.
These shapes work well with conventional manufacturing, but 3D printing is different because it is mostly hollow on the inside
Less filament, yes. But it’s almost always weaker.
It’s common to add holes so you get a stronger part.