Thank you for this interesting question, Błażej Porwoł.
True, the Activity subpage tends to be very crowded as it includes all subtitle revisions created by a given member. So it is indeed a bit awkward to find one's work there. However, having a separate page for the videos you add to Amara is also administratively needed.
So, to simplify finding your work, you could bookmark the subtitle sets you've made / collaborated in. A bit DIY, granted, but in my experience, it works.
Best,
Claude
Błażej Porwoł
It seems that when doing translations for Youtube videos, the only place where I can actually see the list of what I've translated is by going to Profile -> Activity, and extracting data there. Why external videos aren't simply included in the My videos tab?