There is an expression “Kill two birds with one stone”, maybe that's right to describe a team like Dortmund, they buy talented players and hone them into sharpness, when successful before selling them they will target the Bundesliga title, a real example is when in the Klopp era, but this method does not always work every season, after all, developing young talent is not easy, in addition to the appointment of the right coach is also very influential. This season is no exception, Dortmund may not compete competitively with Bayern, obviously because Bayern are in peak form and Dortmund are still building strength with the approach you have mentioned.
Everyone thinks Dortmund does that all the time, but that is not really true. The whole period where they sold Sancho first, Haaland afterwards and Jude later on, it looked like all Dortmund does was getting potential players, make them play a bit and get better and seen, and then they sell those for a lot higher.
Who did they sell last year? Gittens? That's it, nothing big, they did not have that type of player sale last year at all. The year before that? Max sale was 27 million, nothing. And the last year they did great was when they sold Jude, and even that year, Jude was the only player that they sold which made them any money, no other player was sold, second highest sale that year was literally just five million euro.