If you check „re-initialize display“ before you start Jivelite without a connected display, Jivelite should start.
Edit: That only seems to work after booting up the Pi. If you then stop and restart Jivelite, it will no longer work. Only after restarting the system.
Jivelite is a desktop visualization for the Squeezebox Server, so a screen is recommended in any case. It is not intended to operate Jivelite without a display. Do you still use the other Pi with the 7″ display? If so, you can switch the player there to the Pi 4 and use it to control that player.