That's not too bad. My Aorus Waterforce 1080tis don't even put out a display signal under legacy bios. Which my Z97 mobo defaults to with a fresh bios flash or bios reset. It's the main reason I have my old gt730 sitting in there as a PhysX card. And yes, the 1080tis have a stock vbios (but not the 730
My nvme pcie optane os drive also doesn't work under legacy bios. The pcie soundcard out of a mpcie/msata to pcie adapter is fine with it though.
You could set your displays to duplicate in windows display settings, try that, then change the primary (1) display. Not the best chance of working, but is free to try and has worked for me.
Maybe you are lucky and have a different hdmi input in your tv that stays real dead unless it is on and you could switch to that and turn on the hdmi after login? Or maybe you have one of those hdmi switches that you could put somewhere convenient and disconnect the signal? I'm assuming that the problem is solved if the hdmi is unplugged from the tv here.