Small mouse-cursor on QT-apps on nix on Ubuntu

Hi there,

I am trying out Nix on Ubuntu since I bought a Notebook that is running better with a prebuilt Ubuntu unfortunately. Now I installed QT-apps like Mullvad, Nextcloud-desktop and KeepassXC with nix-env but the mouse cursor is very small when hovering over these apps on my Budgie desktop. When I installed e.g. Nextcloud from the official repository I see a normal-sized mouse cursor.

How do I configure the QT-apps to have a normal-sized mouse-cursor?

Thanks and regards, Timo