Screen glitch when starting up MacBook Pro

[Sirious]

Hi all,
Apologies if this has already been posted, but since updating to Big Sur, my Mac displays the following screen for a second before continuing to boot up as normal.

The recent updates haven't (obviously) fixed it and Im not sure what else to do or whats causing it.

I have a MacBook Pro Mid-2014 Retina.

Any suggestions welcome! Thanks

 

[Spudlicious]

I got the weird impression I could see my face reflected in your screen, complete with the beanie I'm currently wearing; I've just come in and there's a bitterly cold wind in this part of England today.
Instantly I am reminded of an oscilloscope display, the type that would have me groaning that the circuit worked OK in LTspice, but sadly I have nothing useful to offer.