No signal after verbose unless I use mini displayport

[P1LGRIM]

My GPU takes Mini DisplayPort, not standard DisplayPort, and my monitor isn't actually DVI, it's VGA

 

[Lost-Entrepreneur439]

You keep telling only part of the story.

VGA is unsupported, Apple don't use it.
That said, some configurations do work but most don't.

It's not the cause of the issue however, if it was, I wouldn't be getting video in Sierra either, and I'd also be getting video with my HDMI TV, but I don't get video with HDMI on Big Sur, and the VGA works in Sierra (as i am using an adapter)

 

[P1LGRIM]

It's not the cause of the issue however, if it was, I wouldn't be getting video in Sierra either,

Like I said, some configurations do work but most don't.
Just because VGA works in one OS version does not mean that it will work in another, your logic is flawed.