How about the gui? Does it populate?
Does it load, yes, is it the right option to do, for the unionfs plugin, probably, for the mergerfs plugin probably not, using either plugin whilst they do what they are supposed to do, it cannot warn you of a missing drive, but then again neither can nofail it just allows the system to boot.
Someone said "nofail" is not an option in this case
It is not an option for mergerfs, but it does apply a 'sticking plaster'