I don't think this is true. According to research reported here: https://europeelects.eu/2021/02/18/trustworthy-but-meaningless-votes-a-look-at-how-russians-view-their-own-elections/ 49% of Russians thought that local elections in 2021 were fair, compared to 37% viewing it as unfair.

This is only about local elections, and even though the pollster is independent it may be under pressure, but I think the best evidence we have is that a sizeable number of Russians think Russia is democratic.

You have to wonder why Putin goes to all the effort of holding and falsifying elections if noone in Russia believes in them.