I was trying this and that, and what worked for me was having an external PCIe drive (thunderbolt+nvme). Then booting on another mac involved a series of reboot

I was trying this and that, and what worked for me was having an external PCIe drive (thunderbolt+nvme). Then booting on another mac involved a series of reboots into recovery to pick that drive (no idea what is goong on there) every time the drive was connected to another mac, but, on the whole, I do not remember having troubles. I did not manage to boot from USB drive at all.