Ps4 GigaByte problem?

Good day my problem is the following and yes you have to update your games yes but often says the PS4 it must z.b. 28GB will be deleted although 68GB were free then I delete a Big Game (Batman Arkham Knight) and in the end the Fallout 76 Update 4GB is big. Can someone tell me why that is?

I think this is the memory of the ps4 I'm not 100% sure this would be my only logical explanation for it because I have not made much experience with it because I have 2tb and thus enough space for some.