As @Sirait said, Moukuku might be leaving the Borussia Dortmund squad, and this has been Dortmund's scheme of earning money, which is selling their better players and scouting for more promising young players.
Youssoufa Moukoko might leave Dortmund in future and I am not doubtful about this because I know about their strategy. Moukoko will not be exception if Dortmund need money or receive too good offer, they will not reject to sell Moukoko.
Many star players left Dortmund with profitable transfers for them in the past decade: Sahin, Gundogan, Lewandowski, Gotze, Hummels, Aubameyang, Pulisic, Haaland, Sancho. Reus is the only star player stayed in their club after all and I believe it is because of Reus' loyalty for Dortmund as well as his injuries. If Reus did not get too many injuries, Dortmund would sell him too.
Moukoko will need a few more seasons to perform better. In this season, he has yet performed at world class level so he does not attract too much interests from big clubs. But he is still young enough and we might see a super star player Moukoko in next few years.