I wrote to support 2 weeks ago and have not yet received a reply. My ticket number is 214697.
Roughly speaking, I'm a bit surprised that so much money is being deducted from my earnings and I can't really find a breakdown in the FAQ and other areas as to why the charges are so high. Yes 10% goes to itch.io and there are a few fees here and there because of PayPal... and according to the tax information on the external site there should be no additional fees. That's why it's currently difficult for me to understand the rather high amount deducted. It is currently far from what I would roughly expect and calculate.