Visible disk
I keep having this discussion.
OF COURSE one could see a visible disk for Jupiter from Mars. After all, I can see it from arth!.
My eyes are good - used to be 40/20, but now dropping to about 30/20. Jupiter is easy as a disk. Venus too. The real fun one is seeing Gibbous Venus as an oblate shape.
if you can do that, your eyes are OK!
(And no I'm not making this up!)