What the fuck man where do I go to have a productive impact

Hell, probably.

Also local city council meetings, but then that's kind of an eternal fool's errand, because those are going to be eternally swamped by the pettiest, most spiteful old people you've ever seen, who are almost always going to overwhelmingly vote against measures which might positively impact your community on the basis that the unworthy might take advantage of it, just like they've been doing for the past 50 years when all the public pools got filled in. It requires more organization and dedication to sit up in city council meetings and trudge through docket after docket of meaningless public works projects and city budgets that you can't affect at all in order to find something that you can vote on, and then figure out that actually your vote didn't matter. It requires a real passion for mediocre bureaucracies.

Also telegram channels, but those are mostly just a bunch of white supremacist dickbags, disillusioned teenagers, and fed honeypots, but then I repeat myself thrice.

Also local volunteer work, but then most of those are just band-aids that further enable neoliberal blood-sucking, and potentially even stifle alternatives, if you're extremely but reasonably cynical, mostly as evidence by the large amounts of neoliberal funding which go towards those sorts of programs.

Probably actually the best answer you're going to find is the worst jobs out there. Something like a local, relatively disorganized or low-key harm reduction group, where you're handing out needles or some such. Something that really nobody likes, basically. Giving out food, shelter, etc. to the homeless (possibly compost toilet or disposal materials, or even doing dump runs for them, helps out a ton), rather than just volunteering at a soup kitchen, or a shelter which probably is either super overcrowded or is subject to too many stipulations, which kinda make them totally useless. Building benches to put at bus stops, that sort of thing. ~~Robbing FDIC ensured ATMs, which theoretically only very minorly increases inflation in an economy which extremely heavily favors the rich already. Actually don't do that one that's illegal.~~ The only problem with those is that it's pretty easy to get arrested for defacing public property, giving out drug paraphenalia, or giving out non-FDA insured food, so, your mileage may vary on all that.

If you're talking more reformist shit, that's stuff where I kind of flame out because I don't know where to begin, but usually it's better done in larger more organized cities, to begin with, it probably involves groups like extinction rebellion, and it involves using more discrete political events, manufactured or otherwise, to push for support and gain leverage against political entities, which can then be transformed into gains, which then lend can itself to more organization. Biggest thing here is probably unionization, so long as it's done for the benefit of workers and not to protect corporations from firebombings. None of those are exactly things that you can sign up for online, usually, they just arise when they arise.