Now to get it working on MAC M1… :)

Is it possible to build with -Dusequadmath on any Mac systems at all ?
I know so little of Mac systems ... beyond claims I've seen stating that they're a "Linux based system".
That being so, I would have thought that the answer to my question would be "yes".
But then, I've also seen lots of scathing remarks wrt "Apple compilers" ... to the extent that I don't really know what to expect.

Using '--64all' dies horribly because the hints/darwin.sh file is missing arm64 and then it gets really confused. But just leaving that off seems to build 64all regardless.

I hope you're talking there about builds done with 64-bit compilers.
Given that a 64-bit compiler must inevitably provide 64-bit IVs and pointers, it might come as no surprise that it is confused by being specifically asked to do something that it intended to do in the first place.
But I would be disappointed if a 32-bit compiler insisted on building a perl with 64-bit IVs and pointers without being specifically asked to do so.

Anyway ... good luck with the -Dusequadmath aspirations !!

Last time I checked, it seemed to me that Raku provided neither 'long double' nor '__float128' support on any systems.
Are we still ahead of them on that score ?

Cheers,
Rob