A bidon is Russian for milk jug, apparently.
When I first heard it, it is what the Russians were calling Biden, to imply that he was an empty container that had to be filled with positions of the day.
It is being used as a pun to insult Biden. Strangely, I’m ok with the Russians insulting Biden.
Along the same lines, Poutine is a French Canadian dish that has three key ingredients==french fries, gravy, and cheese curds (cheese is a poor substitute). However, it is delicious. The empty suit aspect of bidon is rich.