“Believe women” simply means to treat them the same way we treat anyone else reporting a crime, by taking their claim seriously until such time as thorough investigation shows that we shouldn’t. Right now the cultural default is to affirmatively disbelieve women even though the false report rate for sexual violence is somewhere between 2–10%.
Women are certainly capable of shitty behavior, but most of what you’ve identified as toxic femininity is personal shittiness and not “toxic” versions of typically feminine traits. “While the defining characteristics of femininity are not universally identical, some patterns exist: gentleness, empathy, sensitivity, caring, sweetness, compassion, tolerance, nurturance, deference, and succorance are traits that have traditionally been cited as feminine.”
Unhealthy versions of stereotypical masculine traits like assertiveness or independence show up as aggressiveness or extreme self-reliance, which tends to lead to poor relationships and isolation. It’s not that men are inherently worse human beings than women, but historical power imbalances and continued valuing of masculine traits over feminine ones is an issue.
The actual biggest issue with “toxic masculinity” is in policing human beings to fit into some kind of box of acceptable norms (e.g., “a real man is like this; a real women should do X). We are all a blend of traits on a wide spectrum and that should be celebrated and embraced.