Based on my own experience, bus lanes often do create congestion. They created a new bus lane on a street I take every day, and congestion has become a lot worse since then, which is not surprising since the bus lane was created by removing one car lane.
Sure, one bus can transport more people, but first, you have to consider that the average speed of a bus is much lower than cars since they must stop every 100 meters to let people in and out. I'm faster on a bicycle! And the slower people go, the more there will be congestion. Second, and that's the key point, there's much less buses than cars. Where I live, it's about one bus every three or four minutes. So most of the time, the bus lane is not used, which is a complete waste of space.
Anyway the real problem is city planning. Because of traditions, everyone believes that higher density is the way to go. But it is the opposite. We should lower density by spreading out cities. Lower density not only means higher quality of life, but also lower congestion. More particularly, city centers should be eliminated. Office and shops should be spread out. to avoid everyone going at the same place at the same time.