It looks like on 22.04 cosmic you can adjust it under Desktop/Appearance. It has rounded, slightly round, and square.

I am not sure where I saw it, but there might be a Chrome extension that does that.

I think you nailed the difference between interactions, especially negative interactions. When people disagree on here they are more forthcoming on having a conversation or going separate ways. Twitter seems like it's built on hate, and its algorithm seems to point you in that direction.