As far as 2010-present, such that the composer is still living, you could probably group the 'big dogs' into three chunks:
1) The Living Legends (Ferneyhough, Finnissy, Sciarrino, Kurtag, Haas, Saariaho, Lachenmann, Dufourt, Murail, Dumitrescu, Ades, Levinas etc.)
2) The 2nd wave spectralists, who aren't always necessarily 'actual spectralists', not that any composer ever likes getting pigeonholed with those sorts of labels (Feinberg, Steinke, Casale, Adamek, Avram, Francesconi, Gervasoni, Neuwirth etc.) This is where the energy was at from like 2010-2016.
3) The new wave of women composers (not including Saariaho or Neuwirth, possibly Chin and Avram, who were already well-established) - basically since Trump was elected the new music scene has been FIERCELY and with extreme focus promoting its women composers, trying to make up for lost time (Chin, Saunders, Firsova, Czernowin, Stulginska, la Barbara, Paredes, etc.) The labels haven't caught up, but that's what's going on in the halls rn.
There was also a brief but intense interest in Asian composers, though it seems like Fujikura is the only one who walked away from that with a big career (Chin and Ge were already established).
There are also important composers who don't fit in any of those categories working in New Complexity (e.g. Cassidy, Aperghis), new simplicity (Zimmermann), musique concrete (e.g. Ablinger) or with some folk influence (e.g. Ge or Alizadeh). There are also some composers still working in the serialist tradition, usually associated with IRCAM, like Manoury, Lucier or Pousseur, any of whom could also probably squeeze in under the 'living legend' umbrella. Just start trawling the new music youtube channels and find what you like.
But you're aware that many important composers have died fairly recently, right? The past few years have been rough, you'd be missing out on Dutilleux, Boulez, Rzewski (only died like a month ago) and Halffter (a few months ago) first and foremost.
Topic: 21 century composers?