Instant deletion of all Photos from iCloud (not using the Photos App on the Mac or iPhone)

I use several devices (iPhone 14 Pro and 15 Pro, iPad Pro, MacBook Pro) and over time, my iCloud (using the 6TB plan) has filled up with a lot of photos, which I neither need nor want in continuous sync on all devices.

I downloaded all the contents to an offline storage medium (Export to large external HDD via Photos app on the MacBook)

No I want to delete all the photos from the iCloud Photo Library. As I want to continue using the (now offline) Photo Libary on the MacBook, deleting all Photos there while in Sync is not an option. Selecting all (~600k) photos on the iPhone without a "Select All" button is not practicable. Is there any "delete all" option on the iCloud web interface or via the Mac/iPhone System Settings?

Alternatively, I plan to de-activate the Photo Library function in iCloud in order to delete all Photos from iCloud. Is it possible to re-activate iCloud Photos *without* restoring all the old photos but just using it as a vanilla new iCloud photo storage? And will storage space be freed immediately when deactivating iCloud photos or only after 30 days?

Kind Regards