I have a Samsung phone and am always having this problem.
Forgive me if you have already done this, but have you deleted all your Whats App sent items, including photos? That can take up a lot of storage.
Any photos on Whatsapp have to be taken off and stored on another device. Also, I go through my gallery and delete any rubbish that's on it. For example, my daughter is always sending me images of things she thinks I may like and friends keep sending my amusing not Covid videos, which fill up my phone.
Once you get rid of all the clutter, your phone should work fine.