I haven't solved it, but at least now I can see what dyld is doing.

Also reproduced on 26.3 arm64. It seems to depend on the library in DYLD_INSERT_LIBRARIES. I tried the curses dylib and that worked. Maybe dyld doesn't like the Valgrind core shared lib and is treating it a bit like a setuid exe?

I've only tested on 12 and 13, I don't yet have access to anything more recent for Intel. For arm64 I do have a mac mini m4. Arm64 is another problem.