Can you display the GRUB menu (listing all the installed kernels),
when you
repeatedly press F8 after starting the laptop?
I tried, and as far as I could tell repeatedly pressing F8 did not display the GRUB menu.
I started pressing as soon as I selected the partition.
(A question is whether Mac keyboard actually sends F8 by default,
perhaps connect an external one).
I don't think it does by default, but pressing F8 when booting Fedora 39 does display
the GRUB menu.
If you decide to reinstall F39 on that laptop, I'd recommend
just
continuing testing with Rawhide ISOs, so that you don't break your system
again needlessly. The ISO needs to boot, that's a prerequisite. If it
doesn't, please file a bug and link it here, we'll make it a blocker bug
for Fedora 40.
Sure, here is the report:
https://bugzilla.redhat.com/show_bug.cgi?id=2245371
Thanks for testing.
My pleasure!