Haha I know that much xD. I'm trying to find out if there are any similarities in interests and focus straight from the horse's mouth. As opposed to going off of the general online descriptions. I have two ISFP friends who say they don't know what they like, I'm not exactly sure what to do with them.
But that's like saying all ISFJs like doing housework and teaching kindergarten. However, it would probably be safe to go with music and movies, maybe possibly things like art museums or physical activities like bike riding or swimming...some ISFPs are athletic, others are visual artists, some are photographers, others are obsessed with video games, then there are fashionistas, cooks, etc.
If your ISFP friends don't know what they like, I'd guess they're Enneagram 9s, and not the healthiest ones in the world.
I'd stick with aesthetic experiences, like I said, music and movies, or going to do something fun like go to the beach or whatever.
I'd say they need to feel accepted as they are, have their deepest values respected, and also be given a certain amount of freedom and space, as well as forgiveness for whatever impulsive or lazy traits they may have.