You are right that fractional shares typically don't come with voting rights.

But: if there was demand, Robinhood could totally offer fractional shares with voting rights.

For each vote, there's typically only a finite number of possibilities.

So Robinhood could just pool the voting intentions for everyone with factional shares, and then vote the whole shares accordingly.

(To be really nice, Robinhood would just own a small handful of extra shares, so that they can round up those pooled votes to full integers.)