Installer hangs on iMac Pro (2017)

[Raffaele Candeliere]

Hi,
I'm trying to install Ubuntu on an iMac Pro 2017 (32GB Ram, 1TB SSD, Radeon Pro Vega 64 with 16GB VRam) using the latest desktop ISO (ubuntu-19.04-desktop-amd64.iso) but the installer hangs very early.

Steps to reproduce

1) Burn the ISO to a DVD or USB stick

2) From the system (EFI) OS chooser select the CD or USB device with the Ubuntu distribution. The GRUB screen correctly pops up.

3) Select "Install Ubuntu" (or "Try Ubuntu", or "Install Ubuntu (Safe graphics)", or "Try Ubuntu (Safe graphics)", the result is always the same) and hit the Enter Key

Expected behavior: The installation process should start

Actual behavior: The screen goes fully blank and the system freezes

Since the system hangs so early, I'm not sure the culprit is Ubiquity or the kernel

[Raffaele Candeliere (caraffande)]

(UPDATE)
I've tried with Ubuntu 18. Even worse. Instead of GRUB, Apple's "Boot Recovery Assistant" kicks in saying that, in order to boot from the chosen media, a software update is needed.
And even in the case when you opt for the software update, upon next reboot nothing changes. The Boot Recovery Assistant kicks in again and again.
Conclusion: at the moment Ubuntu cannot be installed on an iMac Pro (32GB Ram, 1TB SSD, Radeon Pro Vega 64 with 16GB VRam)