"Documentation" in my mind does have an audience that you hope can benefit from what you are writing. The difference between that and journaling is that you need to define what this audience is like, their starting point and interest, and then write in a way that dovetails with that.

Maybe like this: journaling is an exploration that takes you from where you are to some hopefully elevated but not-known point. Documentation takes your reader from where they are to where you want them to get to.

Or like this: only you can assess the quality of journaling. Only your audience can assess the quality of your documentation.

(and I guess the audience can be yourself in the future. EG, I figured out the wiring schematic for my house and I am going to document it for myself in the future so I can get to this point of understanding quicker. But that still has an author-audience relationship, the future version of yourself might say "what the fuck was I thinking when I wrote this, this doesn't make any sense for my wiring needs" whereas that expectation wouldn't exist for a journal)