I didn’t have to recompile nixnote2. I just needed to complete my system-update via yay, which was updating something about JavaScript (qt5-webkit). i even couldn’t find any intervention in the nixnote packages, although it took 3 hours.
Btw i used the nixnote2-git-version, because the normal nixnote2-package didn’t work, so was actually happy to find the right version and am still satisfied.
Thanks anyway for your participation and the tip.