As a straight female "quirky" NT who has had serious relationships with neurodiverse (first one AS, current one OCD), nerdy, non-alpha males - in other words, guys an awful lot like many of the members of this forum - I'll weigh in on this.
The difference between a genuinely nice guy and a fake Nice Guy is, in short, whether or not they remain nice no matter what happens. The real thing approaches the woman of interest with an open mind, does eventually get around to asking the woman in question out, and may be hurt, but will not go on a vengeful rampage, if the answer is no or the relationship one day breaks up. The fake Nice Guys that the Social Justice Warrior community complains about, on the other hand, react to rejection by swearing that all women must like alpha-male A-holes, and will therefore swear to turn themselves into one in order to pursue success with women.
I know that I have never dated a fake Nice Guy, because my ex-boyfriend did not become an alpha male A-hole when I broke up with him, and my current boyfriend did not become an alpha-male A-hole when his first serious girlfriend dumped him or when an unrequited crush of his after that was revealed not to like him back. These men remained decent human beings.
So if you are worried about whether you're a fake Nice Guy (tm) or not, ask yourself that question: if the woman of your dreams rejected you, would you react by assuming that all women must therefore like jerks, and try to become a jerk yourself? If so, you are indeed one of these fake Nice Guys (tm). If you would react instead by finding your favorite way to numb psychological pain while it lasts, moving on with your life, not swearing to seek vengeance or change your personality, and being open to other opportunities and treating potential future partners as unique people who deserve to be treated well until proven unworthy of it, then you are an actual nice guy, and if any Social Justice Warrior mistakes you for the first kind of guy, then they are wrong and they are not ready to date a genuine article who has much to offer like you do.
Good luck!