Make sure it is executable: sudo chmod +x /etc/xdg/autostart/81-openproject.desktop. Also consider putting it in ~/.config/autostart. One more also that you can make this thing a systemd service and enable it.
You probably don’t need sudo anywhere in the alias.
KDE asks me if a trust the file or not before running. But making the .desktop file executable removes that step. Anyway @xps you can go through this Docker - ArchWiki