this is not that relevant here, navalny himself isn't that involved in the political process per se, as in he doesn't run for state duma or for other legislative bodies, because it's very unlikely he will be let to participate, especially so looking at the recent developments, but he and the fbk are "brewing" a lot of other candidness for various legislative positions, that is FBK supports them in various ways: helping promote them, offering legal help, helping to collect signatures to participate in elections etc etc

he himself may not be popular with the general population, but the majority of russians are fed up with their living conditions, which is shown by the declining rates of support for united russia (the current ruling party), and as a result people are ready to vote for literally anyone else besides united russia members, which is where the aforementioned candidates come in, who have a solid program of action etc etc, and this is for whom people do actually vote

the presidential role is not that important in this case, in the sense that the opposition in russia is focused on occupying and controlling smaller scale, more local government positions, which would in turn allow them to work up the chain so to speak by having more control over making sure the elections are fair etc etc