I mean, the 80/20 rule is seen in all kinds of places. Probably the top 20% [0] of men are involved in the 80% of heterosexual sexual couplings, with the remaining 80% of men being involved in the other 80%.
Where the stat kind of fails flat is that the same is true of the top 20% of women.
That said, the model (with no statement being made of how much that model reflects reality) being described is sequential monogamy. One of the top 20% men will continuously have one or two partners, switching them out for new ones; the rest of the men will only rarely get a partner; and women will fall between those two. Matching them percentile-to-percentile, the average number of new partners in some timespan for a given percentile for women will be larger for women than for men, up until some crossover percentile X% at which point men will have more partners.
I do think that if a person's primary mode of dating is through online apps, they end up with a skewed mental model of what dating is like. They are, however, already the main mode of new relationships being formed, and perhaps are still increasing in importance.
[0] "Top 20%" being defined as the 20% of men who have the most sexual partners