The way Dortmund find players for their team is very much clear to me, they are investing in younger players and talents like Jude Bellingham and Haaland this way they find talents they need for their teams and then after investing just a few amounts of money on these players, they can sell players for a huge amount of money, just like what they did with these two players recently.
Dortmund did quite a great signing in every transfer window as they were able to see the potential of their target player in the transfer window. If you look at it, Dortmund did not spend a lot of money in signing players because they bought players from teams that were not well known. I think the investment they make always profit off in every transfer window.
Dortmund income from the sale of Bellingham to Real Madrid is enormous. So that Dortmund can bring in many players in the transfer window this season. In fact, every player signing that is done by Dortmund always surprises us because they bring in players from leagues that are not famous for cheap prices.