Haiku 64-bit boots natively on my iMac (Retina 5K, 27-inch, Late 2017).
rEFInd is not needed.
Made an USB Stick with the nightly and install to an other USB Stick in order to get more space.
The Haiku Guides were a big help.
https://www.haiku-os.org/guides/uefi_booting
Graphics is Vesa at 3840x2160 not 5120 x 2880 Pixel. Tried a vesa file with different settings in /kernel/drivers with no success.
LAN works, WLAN does not. Sound is recognized but does not work. It is nice that the Bluetooth mouse and keyboard works out of the box.