It gets better if you backup and then get the prompt again after the next feature update of windows - because you get asked again and if you click on it will do a second backup which means that now all files are twice in your OneDrive, then three times, then four times, then… a reminder to upgrade OneDrive further as your storage is full.
I had to clean up this less more than once now for people and even witnessed it live after doing the upgrade for them sigh