IBM open sources fully-functional Lego microscope design (2020)
The main reason the guy built this was so he could photograph certain kinds of specimens on an angle and reduce glare.  It seems like a fairly specialized use case.If you just want or need to look at stuff under a microscope, it's probably better just to buy an inexpensive one.  You can get a pretty decent one in the $300-$400 range.  I have one of AM Scope's stereo boom microscopes and works great for what I need it for. It is quality stuff and they have a range of different types of microscopes.