I mean, if you want an answer to that you could just stop using your smartphone for a few weeks and see what your brain comes up with. Here's a short list of some examples that were popular when I was a kid and smartphones did not exist yet:
Magazines, the daily newspaper, books, going out and exploring, shopping at malls, doing a hobby or craft, personal projects, television, chit-chatting with friends or even strangers, video games, puzzles, play with your pets, exercise, play sports, sitting quietly and being alone with your thoughts.
I was getting my vehicle worked over recently. At the time I was listening to a podcast. A couple other people, probably early 50s were chatting. The old dude in the corner, likely around 70-80 was just sitting there hands empty, looking around, reading nothing like some kind of psychopath.
Whoaaa whoa, whoa now. I don't want the block demolished. Psycho old man strength vs shooty patootie police? I was just there for an oil change and to check on some potential damage.
Ah, the panic of having to use the bathroom so severely you can't make it to your book or magazine in time. Oh look, I wonder what Methyllaurelsulfate does?
I always thought the bathroom reader books were tacky and stupid, then a I got a couple and they came in clutch so many times.
Now that I have a phone, I think it's kinda gross to have items out for everyone to touch while using the toilet. Weird how perception changes.
As a kid, we were constantly outside. In the summer, spend all day in the pool. Three seasons, in the woods. Any time, playing with neighbor kids. Winter, skiing, sledding, snow forts
Without doom scrolling, we had time for actual activities. Marathons of Risk or Monopoly. Assembling and painting scale models. Building, fixing, or repairing whatever needed it
When I was about 13 I downloaded a lot of the Simpsons or sort on my phone, which was not a smartphone but still could play videos and songs. Had a lot of great time with that little device.
I'm pretty sure no one knows this phone because I think it was for South Korea only but it had dedicated touch button bar at the bottom for media control. It was so good. I wish that is still a thing..
I watched a lot of TV and browsed the Internet on my desktop. Now I can just do these things while I'm on the go lol although I still do it just the same at home too