Sanders was crushed by Clinton in the 2016 primary elections. It was clear pretty much from the start that she was going to win. You take away all the super delegates, she still demolishes him. Did they show some favoritism towards her? Sure. Did they call him some bad names in private emails? Yes. Did she get a few questions before a debate? Yes. Is there any evidence that the election was rigged and stolen from Sanders? No, none at all.
This insistence that the Sanders was somehow robbed of the 2016 nomination (or 2020 nomination at that) is equivalent to Trump’s claim that he was robbed in 2020.