It can be done, using this solution:
https://community.victronenergy.com/t/recipe-for-booting-venus-os-on-raspi4-from-usb-ssd
Be aware, some of the “quotes” should be replaced, as the author (or the forum software) put the backtick sign and not quotes.
The second aware: updates does not work anymore. You should make these steps again and again for each update. And if you don’t make an backup of the data on your ssd, these will be lost, because you need to format ssd each time.
I’m working on a solution on this problem, but till now, I have already 3 days of pain in the a$$ with this approach, as I cannot find a good way to replace only the boot and root partitions.
Cheers