I admire you for taking the high road. Ideally, your approach will eventually have an impact.

But you might consider an alternative strategy.

• Use the app to post stories about legal action against Nextdoor and similar apps, as well as negative articles like this one. Tell your neighbors you’re providing this information for their own benefit, to protect them from embarrassment and/or legal fees. A little passive-aggressiveness can go a long way with folks like your neighbors.
• Point neighbors to the following statement from National Neighborhood Watch (a division of the National Sheriff’s Association): “due to the large number of neighborhood watch groups across the country, ‘policing’ and investigating them on the national level is not something we have the resources/capability to routinely do. If you have concerns about a neighborhood watch group in your area, please contact your local law enforcement agency.” Encourage members to report suspicious activity by the neighborhood watch group (e.g. racial profiling) to their local law enforcement agency.
• Direct members to Nextdoor’s statement against racial profiling. Do this every time someone posts a race-tinged message. Again, it’s “for their benefit.” Otherwise, you might have to call the police (see above suggestion).
• Go really low and report suspicious behavior by people who “look like Russians” or someone who looks like ________ (name of the most recent white male mass shooter) or people who have suspicious gatherings at all hours. Tell fellow residents that you have installed hidden cameras around the subdivision to catch these suspected felons.

Hope you get positive results from whatever strategy you adopt. Justice is on your side.