How to free up iCloud storage space on my iPhone 11 Pro?

I have an 11 pro, 17.6.1, and my question is that, why my onedrive takes up 250mb in iCloud, and Documents readdle app takes up 200mb? I know i can just turn it off, but what if they store important backup data? I just eant to delete the not important data.

[Re-Titled By Moderator]