To me, the man depicted looks more like Julian the Apostate.
"Battle elephants were associated with Greek armies beginning with Alexander the Great, so this might be a depiction of a Jewish legend about the meeting between Alexander and the Jewish high priest" ~ Professor Jodi Magness, University of North Carolina.
So it is not definitely Alexander the Great.
Battle Elephants also comprised the Persian army that defeated and killed Julian the Apostate.
|Above image from Pinterest. From "Sassanian Elite Cavalry AD 224 - 642" by Dr. Kaveh Farrokh, illustrated by the late Andrew McBride. Osprey Publishing.|
Julian was blonde and as Emperor, bearded, as shown in the AE2 coin from the Antioch mint below:
More importantly, regarding the Jews, he favoured them.
Note also the imperial purple robe the man is wearing in the mosaic.
So a depiction of Alexander the Great, from around 332 BC when he was campaigning in the Levant against the Persians or Julian the Apostate, from around 361 AD when he was campaigning in the Levant and Mesopotamia against the Persians?