Precision 5820 Tower won't boot without a monitor (headless)

Hello,

I have recently setup my Precision 5820 Tower to be accessible from RDP and ssh. However, I it doesn't finish booting unless I have have a monitor connected. I don't really want to have my monitor on and connected to that machine all the time. Is there any way that I can have it boot without needing a monitor?

Incase it is relevant:

I have stop on boot warning and errors disabled in the bios.

When it boots and the monitor is connected it displays: "HEADLESS OPERATION ACTIVE" and can boot without a keyboard, but seems to require a display.

I have an Nvidia RTX A4000 as the graphics card

Have setup Windows 11/Ubuntu 22 Dual boot and neither seem to work

Thanks in advance for any insights you might have.