There are some links that mention this, for example:
Ukranian Euromaidan Press claimed in 2017:
There are now well over one million prostitutes in the Russian Federation, a figure that is higher than the combined total of doctors, farmers, and firemen, official statistics show (snob.ru/selected/entry/128051). Meanwhile according to the leader of the Silver Rose, the unregistered association of Russian sex workers, the number of sex workers in Russia exceeds three million (iz.ru/news/586344).
Meduza claimed in 2019:
According to different estimates, there are between one and three million sex workers in Russia today.
Newsweek reported in 2016:
Official statistics estimate that there are 1 million sex workers in Russia, but Zazhmilin [deputy head of the campaign group Vice Squad] says the figure exceeded 3 million a long time ago.
I'm skeptical about these claims: If true, Russia would have around 208 sex workers per 10,000 population.
For reference, Thailand, considered a sex tourism destination has varied estimates of sex worker population from 43,000-2,800,000, but 200,000 seems to the upper end of the more reliable estimates. That would make a ratio of around 27 sex workers per 10,000 population.