I figured out what created the difference. Most of the crowdlending sites are created like deposit accounts. I have a couple where I buy actual shares. Those are categorised as deposit accounts with a security account. In march I deposit 50.000 to an account - and then I buy a security for 50.000. Then the difference on the two graphs starts gapping with 50.000 more. So the only reason why the two lines are different is the securities bought. Therefore the problem is that it is not just the invested capital, when I put together all the deposit accounts, but also with the interest income and so on.
It can also be seen before 2019, where I only have an investment in one crowdlending site. And thinking about it the two groups before 2019 is completely alike (and therefore the problem i still that I cannot just choose the invested capital for a group.