If you are facing black bars problem for AC Games (Odyssey & Valhalla) & your game runs in a strip in-between your screen, then I might be able to bring a smile to your face. I came across a "Windowed-mode" optimizer which stretches the windowed mode ( the only mode that allows you to adjust your aspect ratio) to the monitor's border's edges & makes it look like fullscreen. This should work for any game that is giving black bars on the screen.
I have been facing this issue with AC Odyssey & had to play it in the strip mode entirely, which was an absolute nightmare experience for me. Origins did not have this issue, started from Odyssey & i have been trying to find a solution since then.
But when Valhalla had the same issue, i snapped & scoured the internet for any possible solution & when i tested in on my system, i thought of sharing with larger community ..
You can see my tutorial on YouYube with this workaround -
Hope this helps someone in need.. Cheers..