I thought about this quite a bit, and I’m not sure swipe-right would be the best solution here. It could easily conflict with native navigation gestures on mobile where horizontal swipes already have other meanings.
I ended up going with a slightly different approach instead. The modal footer can already be dragged down to close it, so I added a small grip to the footer to make that interaction more discoverable.
This way, even if you’re scrolled all the way down to the last post, you can simply drag the footer down to close the modal without having to scroll all the way back to the top or reach up to the top of the modal.
I think this feels a bit more natural for this type of modal.