Somehow my first assessment for 3U is an assignment?????????? how does dat work bruh/
yes, that's normal. my first 3u assessment task in year 11 was an assignment and my second prelim task for 2u was an assignment, and the final assessment tasks for 3u+4u (and 2u as well for those who do it in my school) before the trials is an assignment.
i don't know how other schools do it, but the assignments at my school generally involved a set of questions on the topics we were doing that term where we had a week to do all of them, before handing it in digitally. for example in term 1 last year we were doing the 3u topics of perms and combs, and further functions; the assignment i ended up getting involved drawing a bunch of graphical transformations of curves and then looking through multi-part perms and combs qns (some of them were questions you wouldn't really see in an exam). i think the syllabus also has something about learning how to use technology as an integrated part of the maths course, and my school implemented that into the assignment by making us use graphing software for the further functions topic.
there was one question at the very end i remember that took so long for me to understand (it was perms and combs, and iirc it was pretty annoyingly difficult for me at least)