My iCloud photo storage is full

I just made the switch from an iPhone 8(64gb) to a new iPhone 12 Pro (128gb).

I backed up all my content on iCloud (I pay for 50gb/Mo) and transferred it over to my new iPhone 12.

I had only used about 30gb of storage on my iPhone 8 before transferring it over.

Once I made the full switch I noticed my iCloud storage was full!

Currently my iPhone 12 is saying there are 43.2 gb of storage being used for photos on iCloud when the iPhone is saying there's only 1.56gb being stored on the phone.

Before getting my iPhone 12 I never had issues with my iCloud storage and now I am. Can Some please explain to me why this is happening, and if possible, how to fix it so all my photos are stored on my iPhone and on iCloud?

[Re-Titled by Moderator]