I am unable to get past the Rainbow screen after imaging Ubuntu 20.04 onto a RPI 2B 1.2+ using official Raspberry PI imager, Etcher, W32DiskImager and Disks on a ubuntu laptop.
The Rasberry PI OS works perfectly.
This is happening on two RPIs, so its safe to assume that my PSU and all hardware is functioning.
I am unable to get v18 Ubuntu working, also with the same results.
On both boards I have done an rpi-update after installing RPI OS so the firmware should be the latest available.
I appreciate this is "old" hardware but as Ubuntu supports it, it should work.
The FS for the RPI OS and Ubuntu are significantly different, the latter missing the kernel7.img file which would be used for the board I have and the Raspberry PI docs including this file in the docs as being used to boot the device.
Information is virtually none existant on the ground for the RPI 2.
If possible a checklist of things to try would be useful.