The traditional way to advertise niche products is to advertise in places where the relevant audience is. Maybe put ads on RC-related websites or technology-related TV channels, or buy sponsor spots on technology podcasts or YouTube-channels. You don't _need_ huge amounts of information about every Internet-using individual in order to do targeted advertising.

Podcasts, which (so far) have mostly been free from extreme privacy-violating ad networks, have been doing this for ages; I regularly hear relevant ads for Ting, Linux Academy and Digital Ocean when listening to Linux-podcasts, or for bone conducting headphones, fancy mesh network routers and domain name registrars when listening to general tech podcasts. I also hear ads for PC hardware and VPNs when watching tech YouTube-videos. The ads YouTube itself chooses for me, on the other hand, are generally completely unnecessary and poorly targeted ads for movies I don't want to see or cars or soda.