The screenshots are indeed helpful.
Your next backup requires in excess of 4.82GB, which in addition to the already used 0.7 GB, exceeds your available 5GB of iCloud storage - preventing your iPad from backing-up to iCloud.
Don't forget, when deleted, files are initially moved to the Recently Deleted folder - from which they remain recoverable. Until these files are removed from the Recently Deleted folder, they will continue to occupy available storage.
The free-of-charge 5GB iCloud storage is generally only adequate for basic synchronisation of essential data and services between your Apple devices. If using iCloud for file storage and backups, it is generally necessary to upgrade to Apple's first "paid" iCloud+ storage tier. In the UK (assumed from your screenshots), the first subscription tier is 50GB - this being £0.99 per month (substantially less than a single cup of coffee from a coffee shop). 50GB is generally adequate for many Users.
As a bonus, iCloud+ provides access to other services, such as Private Relay and Hide My Email.
Buy iCloud+ or upgrade your current storage plan – Apple Support (UK)
iCloud+ plans and pricing – Apple Support (UK)