Hey!
I looked into this a lot recently. Sadly, iTunes doesn’t work on Chrome OS directly, especially on ARM-based Chromebooks. Even if you try using Linux (Crostini) and Wine, iTunes won’t detect your iPhone because of missing drivers.
But there’s a tool called idevicerestore that some people use in Linux to restore or downgrade iPhones. It’s a bit technical and only works if you have saved SHSH blobs and the right setup. If you don’t know what those are, you probably don’t have them.
So, for now, the best option is to use a Windows or Mac computer if you need full iTunes features. Hope that helps!