Freeing up space to install latest OS, even though I have 45 GB free!

I'm trying to download and install the latest OS for my 2017 MacBook Air. Currently it's running Monterey OS. It's says there is not enough storage space, but when I view Storage it says I have 45 GB available. I don't get it. Any ideas on how to proceed? I've already cleaned up files, photos, and back stuff up to iCloud despite having enough space to install a 5.9 GB file.