Bodhibuilder works perfectly for bl5.1 in fact I was playing with it earlier as we had some questions on Discord about creating an iso.
Not sure about mint/buntu 20.04, though I think it was designed with earlier Ubuntu’s in mind. I’m sure there will be a bodhibuilder for bl6.0 (based on Ubuntu 20.04) when it is released.
Is it possible to try Bodhibuilder 2.20 for ubuntu 20.04? According to Sourceforge, it should in principle exist from 2019. Or can you direct me to someone who can guess why I can't succeed Bodhibuilder 2.18 with mint 19 with backup mode? As I understand 2.18 should actually work on Ubuntu 18.04 systems.