If you're not a Bernie Bro - which is commonly used to the group as a whole, not the genders of its members - you are certainly sharing the same goal that many Bernie Bros do, to fervently oppose Biden and encourage others to not vote for him.
This week, in the middle of a pandemic that has killed 126,000 Americans (and is on track to kill perhaps that many more), Trump is trying to get SCOTUS to wholly overturn the Affordable Care Act - Obamacare - which would cost about twenty million people their health care, including several in my family.
Biden helped get the ACA passed, and wants to improve it...which means that more people would be covered, not twenty million fewer.
Whatever you may personally want to think, the way our political system is designed, Biden is the only human being who can beat Trump in November.
If you're refusing to vote for Biden, and encouraging others to not vote for Biden, then you are effectively endorsing another four-year term for Trump.
That might not be your intention, but in this sorta-kinda democracy, that binary choice is the ONLY choice we have. If you don't vote for Biden, whatever your *intention* may be, your *action* is effectively an endorsement of another term for Trump.