It doesn't explain how to stop synchronizing folders inside the Documents folder, it explains how to stop syncrhonizing the entire Documents folder. You can't specifically exclude the subfolders Sims 4 incorrectly uses for temporary (scratch) files, like the "c:\Users\[UserName]\OneDrive\Documents\Electronic Arts\The Sims 4\saves\scratch" folder, for example.
And my problem isn't even the space. I have more than enough space on Onedrive. The problem is that since The Sims deletes hundreds of temporary files from the Documents folder when you exit the game, it triggers the anti-malware protection of OneDrive, resulting in annoying messages such as this one:
Thanks for accurately describing what is the same problem that I am having.
