How can I use the NRF24L01 modules without a library?
You can use the NRF24L01 by writing the functionality that is currently within a library yourself (and strip of parts you do not use).

However, for this, you need to understand the library, and therefore high likely the datasheet too.

You also can start without looking at a library, but your only documentation source is the datasheet itself.

A NRF24L01 has a lot of possibilities (that is why the datasheet is so extensive), so writing the functionality yourself might be causing more time.