Edit 04 Feb 2021
In the end I flashed a 16 GB Toshiba MicrSD HC I using etcher, my faith that all will be good, and about 40 hrs of time (Flash Rate 0.1 MB/s as stated by etcher)
This time etcher showed success and the PI powered up and I could proceed with the setup
Being bold, I again flashed the 64GB Sandisc microSD UHS-I with etcher
Again etcher showed me 0.1 MB/s and so I let things happen.
After about 40 hrs etcher again showed success and YES, the ÜPi powered up and things turn out to work good also with a 64GB card which etcher in a previous attempt could not manage to flash.
So the story is:
Using etcher to flash micro SD cards with the PI OS Sirius works on my system
A laptop with SD card port and Linux MInt 20
But it is utter slowly
The unpacked OS is 7.8 GB, the packed/ZIPed file is ~2.2 GB
Use at least a 16GB micro SD card
I dd’d “2021-01-11-raspios-buster-armhf-full.img” on the sd card.
This time the system spun up but stopped because it is missing “pi-top os zip”
How did the raspi os know that?
Now I try to flash Sirius on a different sd card (only 16GB), this time with etcher.
Etcher tells me a transfer rate of astonishingly 0.10 MBit/sec.
I don’t understand why.
But this was that way all the time, with every attempt
All right , lets give this a try:
By some reason I lost the micro SD of my CEED.
The CEED is as it was sold thence with a RASPI 3B+
Now I want to use it with the new software version Sirius
(I was not aware of the Pi-Top  to  until now)
I have brand new 64GB SD cards available and flashed Sirius as of Dec 2020 C781
I noted that using etcher takes a long time, that unpacking the zip file behaves mysteriously slowly. But in the end i was able to flash the sd using dd.
(actually etcher worked out as well, but it told me it would take 2200 minutes to flash.)
I use a laptop running linux mint 20 and the laptop has an sd card port available
The CEED starts with the rainbow screen and then the heart beat stops (The green led)
The screen stays black afterwards
I tried the earlier version of Sirius, C741, having the same issue
I have read that some people are using Sirius with the CEED and not found anyone having the same issue.