mmmm.. parang ang hirap maghanap ng katulad nyan, TS.
harem w/o romance? you mean, yung aware si male mc na maraming female characters yung may gusto sa kanya, but he just don't see them as romantic interests kasi he's more focused sa objectives nya and/or wala syang capacity for romance, or yung tipong si male mc is just dense, di nya pansin na maraming babae nagkakgusto sa kanya?
If yung katulad nung unang option, then:
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Overlord (has LN and Manga) - mc is a skeleton and may 2 characters na obvious na may gusto sa kanya and alam nya yun,but since he's a skeleton and may system na nagka-cancel na makaramdam sya ng kahit anong intense feeling/emotion, so though aware sya dun sa dalawa, hereally can't do anything.
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That Time I got Reincarnated as a Slime (has LN and Manga) - mc is a slime and wala syang gender talaga. So far naka abot na ng Vol 12 yung nabasa ko and walang romance na nangyare, though may 3 girls yung obvious na gusto sya, and another 2 na possible na may feelings sa kanya.
if yung katulad nung second option. Wala ko maisip, well, wala akong na-encounter pa na ganun, kasi umiiwas ako sa mga dense mc's

and harem na din.
Dun sa anti-heroes (though yung alam ko lang is walang romance involved talaga)
- Kill the Hero (Manhwa)
- The Hero Who Seeks Revenge Shall Exterminate with Darkness (Manga)
- Solo Leveling (Manhwa)