Show what's inside each Layer in the Timeline

I was looking at a video on youtube and it somehow could see what was drawn at each layer from the timeline, also the timeline was at the right but I believe I can figure that myself (it’s not that important I think).
Back to the point, how do I enable that feature?
Or is it some kind of modified Aseprite with scripts?

Thanks for your time.

You can find all those settings by clicking this button.image


I somehow missed that option, thank you