Hello, S24 Ultra here. Hopefully this will make sense: a little while ago there appeared a feature in the gallery where when you played motion photos, there was like a seeker / slider bar, kind of like the seek bar that displays on the YouTube video where you can fast forward or rewind. It enabled you to easily select the right picture to extract as a still photo. Does anyone know what I'm talking about? Well, my gallery stopped displaying it, so I can't even screenshot it to post an example of what I'm talking about. I'll post a makeshift example.
At any rate, I don't see that option anymore, and it is bothering me. Is there a way to re-enable it? I'm thinking it was a part of some previous update, but I can't actually remember.
If you click the edit icon then click the left most icon, you can choose the key frame. 
Well, I don't know specifically about motion photos (I don't take them), but I do have some videos. When I open the video and tap at the photo bar below the video, it expands the video and I can move the indicator to a specific spot, then tap the camera icon on the left to capture that particular spot. This may be the new way of doing it. Thanks for the question, I learned something new today.
