I'd like to be able to suggest some group or movement here, but I've never been much of a joiner. The BLM folks I've heard from seem to have good heads on their shoulders, though. You could do a lot worse than to consider their suggestions on the question of "how do I help?"
I definitely do understand feeling powerless. But remember also that, as a middle-class white person, especially if you're male and the head of a conventional family household, that puts you pretty close to America's own idea of what America is. Believe it or not, there's a subtle kind of power in that. Things that might likely be ignored when said by - oh, someone like me, for example, who while also middle-class-ish white is a weird queer redneck loner and always has been - often are taken more seriously when said by someone who presents a gestalt of commonplace American normalcy, simply because of the sort of person who's saying them.
That really is a power all its own. If your social and professional circles are anything like mine, you can often enough find opportunities there to wield that power - gently, of course, and with real care for those with whom you're talking; to be, or to be seen as, a humorless woke thought editor, is to fail - in a way that might help redress injustice in a small way simply by convincing someone else to think about whether they should see the world a little differently from how they have before.
It's a small thing, for sure. And it can on occasion be a risk; if nothing else, to speak honestly from the heart on any subject constitutes a degree of vulnerability, and people don't always treat that kindly. But little in my experience worth doing is entirely unattended by risk, and little in my experience does more to ameliorate a sense of powerlessness than to hear someone say "you've given me a lot to think about", and then to see over time that they have thought about it.
It's subtle, as I said. It's a small thing, and it doesn't always work. But it is something. And even when you fail - which you will, sometimes at least - at least you will have tried, and even in that there's a kind of consolation to be found.
And if you change white to any other color the power that comes from embodying something people consider good is still there. Arguably a race other that white makes it more powerful because in some contexts that would imply successful social/economic mobility.
The power comes from embodying ideals. They're all boxes to check and depending on what square you start on you'll have an easier time checking some boxes than others. If you're a white guy born to a stable middle class family it's gonna be easy for you to get the power that comes from check the boxes that come with a stable middle class family of your own. But you'll never be able to check any of the boxes that come from overcoming the kind of adversity you never faced and climbing the rungs of the social ladder you never had to climb. Who's more respected the plumber who can afford a Corvette or the engineer who can afford the Corvette? Having a nice family in a nice house in a nice suburb won't give you any credibility if that's the kind of life you were born into and getting it yourself was just a case of going through the motions. If you have a nice family in a nice house in a nice suburb and you were born the son of a police officer in French Indochina in 1955 then you clearly put the effort in to get what you have.
It's not about race. It's about who you are and what you've done. Sometimes race can be shorthand for that but unless you are incredibly lucky/unlucky those are not the kind of events that dominate the arc of one's life.
I'd be more inclined to credit what you're saying if I hadn't seen precisely that distinction so often expressed by people who, in contexts not influenced by their perspective on race, uphold pure meritocracy as the highest good, whose primacy is a uniquely American virtue.
And, in any case, people's perceptions aren't as simple as you make them out to be. I think it would be very nice if they were! But to behave in contravention of reality is the best way I know to betray myself into foolishness. Maybe you've had better results with the method.
Do I? I'd be (genuinely) interested to know what kind of power you think I have to change the system. Because from my perspective as a middle class white person I feel just as powerless to change the system as everyone else.