Hey there iSerbian,
To clarify, are you signed in with the same Apple ID when seeing the difference within storage amounts? Also, did you complete a backup after taking the first screenshot where it shows 3.91GB available?
If you try managing the storage, does it reflect in the total amount available? Use the steps below to manage the storage in iCloud, starting with photos:
Open the Photos app, then tap Photos at the bottom of your screen.
Tap Select, and choose one or more photos or videos that you want to delete.
Tap Delete , and then tap Delete Photo.
You can continue managing the storage, (backups, etc.) using this link: Manage your iCloud storage - Apple Support
Take care!