Black screen with 20.10 and 21.04 desktop installers

How do you install, from DVD or from USB storage device?
Have you verified the checksum of the 20.10 and 21.04 installers to make sure that the installer iso files aren't defective?
Do the installers work on other hardware?

What video chip do you have? Is it a switching video chip?

Thanks for your comments. The installers' checksums were of course verified before dd:ing to a USB stick.
 I tried the 21.04 one this morning on a Dell laptop and it could boot fine all the way through to "Try Ubuntu"

The system has embedded & discrete graphics. Here is the info from inxi -Fxxx since it runs a fully updated 20.04 just fine:

System:
  Host: kernow Kernel: 5.8.0-50-generic x86_64 bits: 64 compiler: N/A
  Desktop: Gnome 3.36.7 wm: gnome-shell dm: GDM3 3.36.3
  Distro: Ubuntu 20.04.2 LTS (Focal Fossa)
Machine:
  Type: Laptop System: Micro-Star product: Prestige 15 A10SC v: REV:1.0
  serial: <superuser/root required> Chassis: type: 10
  Mobo: Micro-Star model: MS-16S3 v: REV:1.0
  serial: <superuser/root required> UEFI: American Megatrends
  v: E16S3IMS.108 date: 11/18/2019
Battery:
  ID-1: BAT1 charge: 45.7 Wh condition: 78.5/80.3 Wh (98%) volts: 15.2/15.2
  model: MSI BIF0_9 type: Li-ion serial: N/A status: Discharging
CPU:
  Topology: 6-Core model: Intel Core i7-10710U bits: 64 type: MT MCP
  arch: N/A L2 cache: 12.0 MiB
  flags: avx avx2 lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx
  bogomips: 38399
  Speed: 400 MHz min/max: 400/4700 MHz Core speeds (MHz): 1: 400 2: 400
  3: 400 4: 703 5: 400 6: 400 7: 400 8: 400 9: 400 10: 400 11: 400 12: 400
Graphics:
  Device-1: Intel vendor: Micro-Star MSI driver: i915 v: kernel
  bus ID: 00:02.0 chip ID: 8086:9bca
  Device-2: NVIDIA TU117M [GeForce GTX 1650 Mobile / Max-Q]
  vendor: Micro-Star MSI driver: nouveau v: kernel bus ID: 02:00.0
  chip ID: 10de:1f91
  Display: x11 server: X.Org 1.20.9 driver: nouveau compositor: gnome-shell
  resolution: 3840x2160~60Hz
  OpenGL: renderer: Mesa Intel UHD Graphics (CML GT2) v: 4.6 Mesa 20.2.6
  direct render: Yes
Audio:
  Device-1: Intel vendor: Micro-Star MSI driver: snd_hda_intel v: kernel
  bus ID: 00:1f.3 chip ID: 8086:02c8
  Sound Server: ALSA v: k5.8.0-50-generic
Network:
  Device-1: Intel Wireless-AC 9462 driver: iwlwifi v: kernel port: 4000
  bus ID: 00:14.3 chip ID: 8086:02f0
  IF: wlo1 state: up mac: 34:c9:3d:87:2b:de
Drives:
  Local Storage: total: 953.87 GiB used: 9.85 GiB (1.0%)
  ID-1: /dev/nvme0n1 vendor: Samsung model: MZVLQ1T0HALB-00000
  size: 953.87 GiB speed: 31.6 Gb/s lanes: 4
  rev: FXV7000Q scheme: GPT
Partition:
  ID-1: / size: 670.20 GiB used: 9.61 GiB (1.4%) fs: ext4 dev: /dev/dm-2
  ID-2: /boot size: 739.9 MiB used: 209.7 MiB (28.3%) fs: ext4
  dev: /dev/nvme0n1p6
  ID-3: swap-1 size: 40.00 GiB used: 0 KiB (0.0%) fs: swap dev: /dev/dm-1
Sensors:
  System Temperatures: cpu: 42.0 C mobo: N/A gpu: nouveau temp: 20 C
  Fan Speeds (RPM): N/A
Info:
  Processes: 395 Uptime: 10h 16m Memory: 31.20 GiB used: 1.80 GiB (5.8%)
  Init: systemd v: 245 runlevel: 5 Compilers: gcc: 9.3.0 alt: 9 Shell: bash
  v: 5.0.17 running in: gnome-terminal inxi: 3.0.38

Try the boot option:

nomodeset

Or:

nouveau.nomodeset=1

I had already tried nomodeset and it did not help.
The behaviour with nomodeset or nouveau.nomodeset=1 is slightly different to the original black screen.
After ^X to boot with the modified command line the screen clears and the following message is seen:

 Booting a command list

But then it just hangs on that. So... still hanging.

So.. do you have any other ideas? Clearly there something different between even the latest 20.04.2 and 20.10 but I have no idea where to start to bisect that.
Are there old (eg. RC 20.10) installers? Or a reliable way to recreate them?

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