I have a separate Screenshot folder outside of my The Sims 4 folder.
I clean the original one out occasionally, since I take a lot of screenshots (over 2000 and counting shots for just one save :p ), and it seems to boost the performance of my game.
Nothing should get messed up if you do this, or if you even keep and organize the pictures within your Screenshot folder.
Your framed photos in-game will remain; the only issue I've noticed of pictures disappearing is when it comes to removing the screenshots taken when a Sim uses "Paint From Reference".
Otherwise, your game will be fine.