There is a bug in the linux version with the helmet!
Try dragging her onto the helmet rather than vice versa.
We currently have no clue why this happens.
That's weird, because I'm on Linux and the helmet works mostly fine! Occasionally I have to try a few times, but usually it works first try.I'm on an older version of KDE Plasma, though. Plasma 5.27.10, and using X11 instead of Wayland.