For me, running is consuming enough that my brain can't really operate at 100%, and it's more like 75%. Sometimes this is wonderful because normally my mind tends to go overboard with stuff, but while running my mind doesn't have the appetite to make things heavy and involved.
Another thing is to just stop focusing so much on your inward thoughts and look all around you. Running is a great way to explore and observe an area because you can pick up way more detail than while driving but you can also cover more area than walking.
It also helps to avoid focusing on whether you're done. A watched pot never boils. Asking yourself "how much distance do I have left?" every 2 minutes is sure to make the run seem like it lasts forever.
Everything I see that's changed since the previous run.
Everything I see that's changed since the previous season.
Everything I can feel about my body moving
Everything that's happened that day.
I've done quite a few 2hr+ runs (half marathon to marathon) and 100 mile bike rides, and after a while for me it turns into a psychological game.
Trail running, if you haven't tried it, is much more "stimulating" I might say, depending on where you are there's a lot more focus and attention required to stay on the trail, to stay upright (slipping on mud, ending up in a river), to dodge trees and rocks as required, etc. I personally find there's much more of an aspect of being "in the zone" for trail running, and especially in races, when I miss a turn and have to stop and backtrack, it becomes really obvious that I was in some kind of "flow" state and then got pulled out of it.
Definitely helps to not keep glancing at your watch though.
I do sometimes find I come up with good ideas for work/whatever when running, so it can be a good way to ponder things like that and I’ll sometimes record a short voice memo on my Apple Watch otherwise I forget what I thought of. But after 20 minutes or so I find my mind kind of defaults to blank and I like that!
My favorite have been the Headspace mindful runs[1].
[1]: https://www.headspace.com/meditation/running-meditation