Hey Timon,
first of all, thank you for the purchase!
The content-import xml files do not transfer website settings in WordPress, so you will need to do one additional thing to display the masonry grid on the front page: please go to “Settings -> Reading” admin section, choose the “Static page” from the “Front page displays” setting, and in the respective drop-down choose the “Portfolio” page that should have been imported with the other content. After saving these settings refresh the website – the front page should display portfolio project grid now. Let me know if you face problems with this!
Sincerely,
Andrii / Satori Studio