Hello Chris,
Thank you for your suggestion, it was spot on.
I had to use even older recovery image
recovery-e-1.21-r-20240323388943-dev-oneplus3.img
Another user had the same problem.
The rest was as is described in the howto.
Many thanks, now I am setting everything up. I am so happy, I almost gave up on this because of lack of time to tinker around.