Same as you, especially since I graduated 5 years ago, I sometimes have the feeling that I will get dumber if I don't keep learning some new infomration and also that working has somehow restricted my word to the niche I work in.

But I'm making a conscious effort to go back to fiction, mostly reading books not in my native language and looking for novels with an interesting setting to start with.

A page count would take the fun out of reading imho. I just use goodreads and set a goal for the year. My goal this year was to find novels I actually like, and to search for living fiction authors that I like, since I had a "fiction dry spell" of some years, when I lost all intrest in fiction. I'm happy to say that I did find some authors I like and got back to reading novels.

I strongly suggest that, if you go digital, you steer away from mobile/pc/table. Having trouble retaining information may be directly linked to social media use, multitasking, mental fatigue, poor diet, poor sleep. Physical books and e-readers help you because you don't have the chance to switch to another tab.

Before you try any complicated method, try to set up the room where you read to be quiet, turn off notification or leave your phone in another room, have a soft light, no background noise. You basically need to be quiet and concentrated. It's normal to forget some stuff you read, I read a lot and some books I completely forgot after a month. But at least you'll give your brain quiet time and you get used to focus.