That's what my
link was referring to, the breakdown where Trump got 12% of Bernie voters in 2016. But 75% of them still went for Hillary.
I don't see a reason why the numbers would change too much from that. Trump hasn't done anything to make progressives happy in the last 4 years, and he isn't the "fuck you" outsider vote any more. Biden didn't backstab Bernie, so he might even pick up more of that slice.
My armchair theory is that progressives are not principled in the way they want you to believe. Instead, progressives are very
politically active. They are very motivated to get out and
exercise power, which is why they're rabid about wokeness and over-represented at BLM rallies. Voting is an exercise of power, and they will feel the need to vote for someone, in proportion to the amount of existential angst they are feeling.
If they thought they were screwing someone over with a Trump vote in 2016, they did so; otherwise they fell back into the default faction and pretended they were screwing over Trump himself. I don't see a fired up, angry, ACAB, change-the-world type virtue signaller resisting the urge to signal their hate at Trump this time around.
Of course if you're a black progressive, maybe you sit out because of of the Harris pick. But you already felt disenfranchised and voted in lower turnout anyway. Plus it gives you a good story to take back to the BLM march and cry into a megaphone about being oppressed.