Sorry if this kind of question isn't allowed here, but I'm at my wit's end. VB randomly started launching on startup about 2 weeks ago (on EndeavourOS) and I can't figure out why. There's no shortcut in ~/config/autostart, it isn't in the KDE startup apps list, and I can't find anything virtualbox-related with systemctl either. There's also no setting in the VB app itself. WTF?
To successfully automate a VirtualBox VM to start at boot time, we must ensure we’re running VirtualBox version 5 and above.
By default, after installing VirtualBox, the vboxautostart-service unit file should exist in the /etc/systemd/system/ directory.
Alternatively, for systems missing the vboxautostart service, we can create a custom systemd unit file that will contain our configurations to run VirtualBox on boot. systemd is a system and service manager for most Linux-based OSes.
Didn't see you mention the autostart-service, and the article is recent enough that maybe it was added as part of an update?
Try to exclude it from being restored on KDE startup. There could be something running in the background that keeps getting saved and restored. Go to System Settings, System, Desktop Session, put virtualbox in the ignored applications list. You can also just choose "Start with an empty session" and then relog to see if that stops it from coming back, then you'll know if this is causing your problem or not. Good luck!