You are missing a big part of the puzzle. Covid Vaccines prevent you from contracting the virus
. If you don't get the virus, you can't spread it. This, in itself, is a very good reason that you should get vaccinated.
That being said, the vaccines are somewhere like 90% effective meaning that some vaccinated people will get the virus. And yes, there is a Lancet article suggesting that the small percentage of vaccinated people who are unlucky enough to still get Covid can transmit the virus to other people.
Getting vaccinated has several benefits.
1. It protects you from getting the virus (90% effective).
2. Because of this, it protects society at large because 90% fewer people will have the virus meaning the virus won't spread.
It is true that the small number of vaccinated people who still get covid can transmit the virus. This is not an argument for not getting vaccinated.