Terje, not sure why you are missing bd.udfs. When I run the AppImage, I get:bd.jpbsbd.m2tsbd.shbd.udfsbd.xmludfs
Entered the new BD50-RE disc into the blu-ray burner and entered
dd if=./bd.udfs of=/dev/sr0 bs=2048000
dd: failed to open './bd.udfs': No such file or directory
Tried this also with root access with the same failure.
Looks for me as './bd.udfs' is missing and not created yet.