It seems to be device specific. On my device, WhatsApp fits 2 more chats. I hate meta/insta/fb/etc, but WhatsApp just looks considerably better than Signal. Signal, as I said earlier, just has huge margins and padding. It looks ugly.

Like you, I also want my messenger app to show conversations. Sadly, Signal shows more empty space than conversations. It really needs a compact UI. I invited several friends to Signal and they all left because it looks bad. I know it sounds like nitpicking, but UI/UX IS extremely important. Making the claim “meh, it looks fine” and ignoring people’s perspective is not the way to run an app that is dependent on the number of users, like signal is. If I don’t have anyone with whom to chat, the app is useless. It needs userbase.