A year ago a friend encouraged me to start a podcast about the history of astronomy [0]. Talking to people who have listened to the podcast has been really eye-opening about the difference in comprehension/absorption between creating a podcast vs. listening to it.
I would notice that other podcasters in the "History of..." genre would sometimes say things like "you might remember we talked about such-and-such related thing in Episode 43..." and I would always think "how do they remember that they mentioned this particular detail dozens of episodes back?" But as I've started writing a podcast, I've found that it's a lot easier than I thought it would be. When you're writing the material vs. passively listening to it, you just have a much more intimate memory of everything you've said and it's easy to make connections across the different episodes.
I try to write the episodes to at have a few big points that I repeat throughout so that even someone passively listening will get the main message. But even still when I talk to people, they seem to have enjoyed it, but have a hard time remembering even some of the basic ideas. And I notice this with myself, too, when I listen to podcasts. Sometimes I'll be talking to someone and be reminded of some related story I heard in a podcast at one point, but when I try to recall the details, they're just not there.
So, even though I was certainly aware of it intellectually, I know have a much more visceral appreciation for the fact tha if you want to learn something deeply, there's really no substitute for doing some creative work on the subject.
[0]: Shameless plug: https://songofurania.com/about