Part of the activist left is absolutely voting for Biden; anyone who’s been working for progress in this country and actively working and experiencing success and failure and the hard work that goes with it would I think easily able to see that letting Trump come to power would be such a severe and wide ranging setback to so many of the things they’ve been working for, and the action of just showing up one morning is so trivial in comparison to a lot of the other things they have to do for years to even move the needle by a tiny amount’s worth of difference, that it’s a no brainer.
I think there’s a significant grouping, also, that’s so horrified by his enabling of a genocide that they don’t plan to vote for him. But, their main focus right now is on putting pressure on the Democrats to stop their support for Israel (with apparently a certain small amount of success), and on direct action against the war, not really specifically anything focused on the general election except for a general feeling of disgust at the Democrats.
Depending on what you mean by “hard left,” you may or may not mean those groupings, and may instead mean some other people on the internet who are super vocal (and often seem weirdly fixated on criticizing Biden for a variety of reasons honest or dishonest, not just the war, and on the vital importance of people not voting for him, much more so than other left activist things that they seem not to be as interested in.)