First one I came up with that I was confident hadn’t happened yet was Hangman vs. Ospreay. They have wrestled against each other in some tag matches with New Japan but never in singles.
Another contender would be Swerve vs. Omega
And Kaito Kiyomiya (arguably the best under 30 men’s wrestler in Japan, an incredible talent in Pro Wrestling NOAH) vs. Omega is another contender.
With so many AEW and WWE wrestlers having done work in Japan and ROH/PWG, it makes this a bit difficult coming up with some ideas.
For the women I’d go with Sareee vs. Mercedes Mone