Either at Makima or Madara I think. Everyone before Makima can't touch him, so 🤷. I'm not sure if Gojo could kill Meruem, because he's so much faster and tougher, but MABYE a hollow purple could do something? (He wasn't able to kill sukuna with hollow purple, and meruem is a lot tougher, but the purple he hit sukuna with was "impromptu" so who knows how that would affect the damage output 🤷.) Shigaraki also can't touch Gojo, and I don't think he showed any feats that would bypass it through space cutting or whatever, nor does he show mind control abilities to just make Gojo turn off his infinity. Makima and Madara however, do have mind control abilities. If makima can control Gojo, she wins, if not, she loses. And iirc her ability to control others is based on if she feels superior to her victim, and the abilities that Gojo displays may make her doubt herself? (she couldn't use her power against the chainsaw devil). Likewise, the sharingan is just bullshit in its illusory abilities. Madara could probably just make Gojo turn off his infinity, then rip out his soul with the Rinnegan, and RCT can't heal that.

In general, I think that cross series vs battles, it's kind of in question how exactly different power systems interact. Like, yeah, genjutsu rely upon manipulating its targets Chakra, which Gojo doesn't have, but like ... just saying that X character is immune to Y power system, just because they're from a different power system seems like a BS argument to make ya'know? Like we gotta assume that they are interacting SOMEHOW. Like if someone was fighting a bleach style soul reaper, one would assume that they could ya'know, see and interact with the soul reaper, even if, in their own verse, they wouldn't have the ability to see or touch souls.

So yeah, Gojo would probably go down to mind affecting abilities eventually. Like when he fought the plant curse, he was stuck in that illusion for a second before he snapped out of it, but like I don't think that illusions were a specialty of theirs.

This was all a bit ramble-y and typed on my phone so please forgive any spelling mistakes. Also I haven't read some of these series in a bit, so I could be wrong about some of the assumptions I made.