So, I confirm having boot issues with Ubuntu 20.04 (even directly with the live usb image). The system freezes before reaching the desktop. I tried the official live usb image released at the end of april 2020.
I tried the daily build images of focal (20.04) and groovy (20.10) versions, same issue.
And I also tried with the kernel 5.6 (linux-oem-5.6) and the latest kernel 5.7.7, same issue.
I did not find any other way than passing nomodeset to the kernel to boot Ubuntu successfully. Within the live usb images, the grub menu entry safe graphics passes the nomodeset parameter to the kernel and boots successfully.
That said, if you want to take advantage of all the hardware of your Dell G3 3590 laptop while using Ubuntu, you can go back to the 18.04 version. After fixing a sound issue by hand, it seems to work just fine so far.
https://bugs.launchpad.net/ubuntu/+source/linux-oem-osp1/+bug/1868105 (Acelan KAo's workaround)
BTW, even with Ubuntu 18.04, it was not straight forward because grub of 18.04.4 live usb image failed to display the menu entries. In my case, I had to go back to the version 18.04.2 that I found here:
Once the version 18.04.2 installed and the system updated to the 18.04.4, everything still works fine. The kernel version I run is the 5.3 (it seems that there is no need to use the kernel linux-oem-osp1 which is stuck to the version 5.0).
I give it a try too...
And the situation is even worse... after an upgrade from 18.04 to 20.04.1, Ubuntu was unable to start even with the nomodeset kernel parameter.
Hopefully, I had done a backup image of my installation before upgrade with the Gnome Disk application from a live usb key. And hopefully, the backup/restore feature works like a charm.
That's the first time that I see a computer bricked after an Ubuntu LTS upgrade. Bad point for the quality of this release...
the solution on this thread works for me.
"Instead of "nomodeset" you can use "snd_hda_intel.dmic_detect=0" to make sound work but microphone won't work."
Like his said, only mic not fine, but using headphones/headset for me it's ok.
Now using Ubuntu 20.04.1.
Thank you so much Daniel for this tip!
I managed to start a 20.04.1 live usb successfully with the parameter related to the microphone.
This workaround is totally acceptable to me, when I need to call someone I use a headset, so I'll attempt an upgrade from 18.04 to 20.04.1 next week.