How can I restore my iOS 17 backup when downgrading from iOS 18?

So on my Iphone 15 pro I installed ios 18 a few months ago but did a backup before that. But now I wanna unninstal so I entered recovery mode with a mac and reinstalled ios 17. But after I went through the setup process I tried to recover my data from an Icloud backup and the only one I had was from yesterday and it made me reinstall ios 18. Is there any way for me to downgrade without losing all of my data?

[Re-Titled by Moderator]