how much storage i need to upgrade to iOS Monterey

Apple doesn't make this specific info easy to find.

But there is this: macOS Monterey is compatible with these computers - Apple Support

I also found this article from a third party that says to upgrade macOS from Catalina to Monterey you'll need about 26GB of free storage space. This sounds about right to me.

https://www.manageengine.com/patch-management/how-to/upgrade-to-monterey.html#:~:text=macOS%20Monterey%20Requirements&text=If%20you%20are%20upgrading%20from,GB%20RAM%20memory%20is%20required.