Files and photos deleted from iCloud are initially moved to the Recently Deleted folder - from where they can be undeleted/recovered. As such, deleted files continue to occupy iCloud storage space until they are either automatically removed (typically after 30 days) or manually deleted from the Recently Deleted folder.
You can recover deleted files and photos (or permanently delete them) by signing-in to iCloud using web browser:
https://icloud.com
The iCloud User Guide provides more details. Here is a direct link to the Guide to get you started:
Recover recently deleted iCloud Drive files in iCloud for Windows - Apple Support
Unless you subscribe to Apple’s “paid” iCloud storage plans, you only have 5GB of iCloud storage - which may be inadequate for your storage needs. For a small monthly subscription, you can opt for 50GB, 200GB, 2TB or more of iCloud storage.
Manage your iCloud storage - Apple Support
Upgrade to iCloud+ - Apple Support
iCloud+ plans and pricing - Apple Support