Hey there, scissors can wear your hand down if you don't have a really sharp good pair, and even then you have to switch scissors sizes to do more intricate cuts as it gets smaller and smaller.
Let me introduce you to the tool that can do all of the above, is cheap, and cuts through cardboard like butter: amazon link
You could probably get a used one somewhere for dirt cheap too if you search around your area.
Edit: Edit to add that i use 2/0 size saw blades for cutting cardboard.