The money that raised from selling haaland and bellingham being used to paid its expenses. The profit can be considered as good enough but it's not as big as you said. It's been reported by dortmund's financial report.
Dortmund is trying to hunt another young talented player to be developed again. I think that you will be seeing some names to join in the dortmund soon. Some names being targeted by the club this time.
In Europe, Dortmund are like Porto and Sevilla which have very good scout teams so that they can find many youth talented players around the world especially from Latin American nations and African nations to buy when those youth players are very cheap. Then they grow those players up and turn them to be star players and sell those new rising star players with expensive prices.
In the last twenty years, Dortmund are very successful with this strategy and they maintain it with acceptable good results in Bundesliga and Champions League. Obviously with this strategy, they are unable to win Bundesliga too often and especially unable to win Champions League. Anyway, winning big titles are not their priorities.
Agree with you that winning trophies is not a priority for Dortmund, recruiting young talents with lower market value is their specialty and then selling them at high prices, this will give Dormund a big advantage. What doesn't make sense to me the most is that they like to sell their players to rival clubs like Munchen. You can imagine how disappointed their fans were to see the direction of the club's policy with such a business style.
sometimes I think Bayern Munchen can win the Bundesliga Trophy without getting significant resistance from other clubs in the domestic league. However the fact that Dortmund is a club with a tradition of selling their star players and that has stuck with them is very convincing.