“Note that only scale transforms are currently handled correctly; rotate transforms are not handled correctly . This is because our popup positioning API (which comes from Wayland) makes applying rotate transforms rather difficult as the popup position is based on a Rect on the parent window. It will probably be possible to correctly handle rotate transforms here, but should probably be done in a separate PR if anyone fancies tackling it - as it may be tricky.”
While as of now this is an open issue, someone has commented on a possible solution for it, see the last comment from August 29th, 2023. However, this probably will require building a custom version of the Avalonia framework itself.