Bernie Sanders (since you're presumably talking about the US) doesn't even support open immigration or H-1Bs, let alone open borders.
I think 'liberal progressives' that are mainly concerned with identity representation, not working class power, are rhetorically bundled as 'far-left'. To people who buy that, Bernie Sanders (a Leftist) and Kamala Harris (a Third Way liberal progressive) are both far-left. It's incoherent but rhetorically potent.
and that's before the boring stuff that drives migration everywhere and always, wage gaps, no economy, dead farmland, family already abroad, the same reasons europeans showed up in the americas by the tens of millions without anyone filing it under "desire." you can have a real argument about capacity and integration, how many people a system absorbs and how fast, thats legitimate. but "it's the far-left's desire" mistakes the symptom for the cause, the people making that trip have their own reasons that have nothing to do with anyone's domestic politics
To think “the west” could make so many messes and not worry about cleaning up after ourselves - the absolute hubris!