Thanks, ah, that was the missing piece! I didn’t notice the issue because this setting was disabled… sorry @satonotdead 
So the issue was that Horizon, in high context topic card mode, does not render the topic-list-item-before plugin outlet, so the theme component could not work.
I moved it to other plugin outlet, it works fine now.
Thanks, I’ve fixed it.
Hmm, I’m thinking about this. How do you imagine this working? Should it work on /latest as well (checking the exact topic category) or only inside the selected category? Should suggested topics in that category also keep the modal?