My fault. Why did I not see that? Too upset at the compositor, I guess. Oops and thank you for pointing that out for me!
Weirdly, I think now I’m seeing what @madmatt was seeing, only I used the Float Full option…
Lots of yellow and green on different objects next to each other, instead of blue and red that would separate them more easily… (cryptomatte layers don’t seem to work for me, but that may be an Affinity issue, so I only get one usable “clown” layer and the rest are black).