Trying to clear photo storage from my iPhone 12 Pro

See if a Forced Restart helps --> Force restart iPhone - Apple Support

It's also possible that even removing 50 videos didn't free up enough space to do whatever it is you're trying to accomplish. One thing you need to seriously consider is the next time you buy an iPhone, buy one with more memory as clearly the one you own doesn't have enough memory to meet your storage needs.

Do you have a lot of photos and videos?

Are you using iCloud Photos – with "Optimize iPhone Storage" enabled on the iPhone?

If your photo and video library is so big that your iPhone cannot hold everything, that might be the issue. You fill device storage, the iPhone sees that you are running out – and replaces some local copies of photos and videos with lower-quality "space-saving" versions. You free device storage – and maybe the iPhone thinks that this is a signal to download full-size versions from iCloud. It might be trying to store as much of your Photo Library as it can, on your phone, without filling the phone to the point of overflow.

Just a guess - I've never filled the storage on my phone enough to see how it would behave in this circumstance.

Try and go the the recently deleted folder, and delete them there to delete them permanently and to make iPhone storage free