Here are some examples of mostly extant classical composers whose works that require either the human voice or few instruments beyond it. I think that these are both appreciated by classical music aficionados and music critics, and I have sung every one of them in a "recent" (mostly pre-covid) concert:
– Ēriks Ešenvalds, a Latvian composer – e.g. https://www.youtube.com/watch?v=jh09QDoJMMg
– Tõnu Kõrvits, an Estonian composer – in this piece of music he echoes another famous Estonian composer, Cyrillus Kreek (d. 1962) – https://www.youtube.com/watch?v=yETJdX5r80U
– Franz Biebl (died 2001), a German composer – e.g. https://www.youtube.com/watch?v=41KBZsdC2dw
– Rihards Dubra, a(nother) lovely Latvian composer – e.g. https://www.youtube.com/watch?v=28NzGYAvsoQ
– Vytautas Miškinis, an excellent Lithuanian composer (b. 1954) – e.g. https://www.youtube.com/watch?v=cBGoPpebOkA
– Andrej Makor, a Slovenian composer – e.g. https://www.youtube.com/watch?v=kYsMU_tc7uU
– Moses Hogan (died 2003), a composer from the southern US, where gospel stretches the definition of "classical" a little bit but to excellent results – e.g. https://www.youtube.com/watch?v=2b-d-JsQhzI
– Vaclovas Augustinas, yet another excellent Lithuanian composer – I LOVE Tykus Tykus (https://www.youtube.com/watch?v=9G8DZD7IFZs)
I think I'll stop here, but this is just a list of the lesser known contemporary famous classical composers in the variety of classical music that I like. The "actually famous" ones – Eric Whitacre, John Rutter, Arvo Pärt, Gabriel Jackson, Cecilla McDowell, Ola Gjeilo etc., or even people like Christopher Tin (who wrote the excellent Baba Yetu, which I think many HN readers / fans of Civ 4 might recall [1]) – have massive followings and, to my ear at least, compose interesting, harmonic and often frankly beautiful music.