I want to create some custom LEGO Technic pieces, but I can't seem to find any software that is good at making it. I have tried using Blender, but it is hard to create holes.
Do you have any suggestions?
I'm sorry you've been frustrated with Blender. It is complicated and not as intuitive as it could be, but the alternatives are vastly more expensive for slightly better UX. 3D modeling is a lot of learning, regardless of the tool. Blender seems to be the best free general 3D modeling package available. There are tons of tutorials out there and Blender.SE for specific questions.
You might find working with Blender is easier if you have exported parts from something LEGO-compatible like Mecabricks. Export a few Technics bricks and beams and hopefully you can figure out how to cut and paste the sections you need. Mecabricks also exports STL, OBJ, and DAE files if you want to work with the proprietary 3d modeling packages.
Or you may find it easier to do the bulk of your modeling in Mecabricks and then make a few customizations in Blender.