The Notes App without any notes does not take a lot of space, so keeping the Notes and deleting the App won’t reclaim much space.
One solution is to move your notes to your Mac (saved locally on your Mac), turn of Notes in iCloud and then delete the iOS/iPadOS App. Then on iOS, look in iCloud->Manage Storage. As you have moved Notes to your Mac, and deleted the Notes App, there should not be any space allocated to Notes. If there is, delete it.
I had a problem with Notes taking up a lot of space and my issue was that I had recently inadvertently copied an App to Notes. I deleted the Note, but iCloud never released that Note from storage.
I solved my problem by:
1) On my MacBook, Moved all Notes from iCloud to On My Mac
2) In System Preferences, iCloud, turned Off Notes
3) On all my iOS devices, turned Off Notes from iCloud
4) On my MacBook,, looked into ~/Library/Group Containers/group.com.apple.notes/ and in the Accounts/LocalAccount/Media Folder, looked for large files and found the offending file attachment is still there.
5) Deleted the offending files in the Accounts/LocalAccount/Media Folder
6) Then looked in iCloud->Manage Storage and deleted Notes (there shouldn’t be anything there as I already moved all Notes to my Mac)
7) Moved the Notes previously moved in 1) to my MacBook back to iCloud