If an action in Special:Contributions is the most recent action for that page (topic), the line should be labelled with "(current)".
Many editors use this feature, to see if anyone has replied to their posts (or elsewhere on the page) in discussions (as well as articles/etc.
For editors who don't use the Echo functionality in Flow, (and in the future, for editors who tweak the 'volume' via T100528: Improve organization and control for Flow notifications (tracking + ideas)) this feature will continue to be useful.

(I can't find any documentation about uctop, in mw.o? That is what uselang=qqx calls it.)

See existing translations: https://translatewiki.net/w/i.php?title=Special%3ATranslations&message=Uctop&namespace=8

Reported at https://www.mediawiki.org/w/index.php?title=Talk:Flow&topic_postId=rw13viyncs80kutq&workflow=rw1343yt60n6dba9#flow-post-rw13viyncs80kutq
and at https://en.wikipedia.org/w/index.php?title=Topic:Sl0n5xte881pqpz9&topic_showPostId=sl0ohbjjdvueysgv#flow-post-sl0ohbjjdvueysgv

In this screenshot, the most recent post to the topic (mine) should have the "(current)" added.