hi i didnt look at the map but here, i guess this is for myself now
1. illegal maps.
if by this, you mean maps which infringe copyright (illegal in front of the law), then you would probably redirect this to the copyright owner. seriously though are you gonna report infringement in a rhythm game?... well i mean, sure fine. everyone has their opinions.
2. farm/impossible maps.
CATEGORY A: graveyarded farm maps
these dont exist. cant farm what cant give pp.
CATEGORY B: graveyarded impossible maps.
these maps pose no issue, since (1) its graveyarded, meaning the mapper does not care for it, and (2) no one recognized the map to be of quality. this quality overlooked includes playability. however, since no one cares, it should pose no problem. someday, it will vanish.
CATEGORY C: ranked farm maps.
these supposed "farm maps" are completely acceptable in the eyes of the ranking criteria and in the eyes of the most basic, generic map quality standards. you can do nothing about these unless you rank something called the Ultimate PP Compilation.
CATEGORY D: ranked impossible maps. you might be talking about tech maps, which are impossible aesthetics maps (there are easy techmaps, but im only pointing out the legit "impossible" ones like, uh, Atmosphere 2). maybe you just dont have the skill to pass these. if legitimately impossible though, quality comes into question. if its ranked, then playability was considered by the BNs to be okay. another possibility you might be talking about is movement mapping, which are impossible anti-aesthetics maps. again, since it is ranked quality of such has already been questioned, and somehow it passed the group.
other types of map reporting...
3. disqualification of a qualified map with a supposed mistake or problem.
just post a problem feedback in the modding section, and it should automatically come to the notice of bns. you cant disqualify yourself though.
your map falls probably under category b. therefore, no relevant player in the mapping process of the map is gonna touch that anytime soon. you cant do much about it.
tldr: in terms of reporting maps, as long as you know who to report to, believe what you believe and do what you wanna do regarding that map. just know that other people work on the same mindset, which is why some reportable maps, if you deem so, pass for others.