When Ozan left Stuttgart - he had a low release clause, and a few clubs where after him - being a big prospect who just had won ‘rookie of the year’ in Bundesliga. The main one being Bayern Munich - with his agent having been in Munich for talks, they saw him as their replacment for Mats Hummels long term.
So there was a bit of surprise when he choose Schalke, although of course, it did make sense, as he saw himself getting more games there from the start.
West Ham and AC Milan where thought to be the other 2 clubs along with Bayern and Schalke that offered the realease clause fee for him.