I have a 3440 x 1440 screen, when I had the project in 4.27, even the main menu, which was just an image, had a very very very low framerate. I never got around to investigating why this was because I moved to 5.3 and it stopped happening. I can’t help you, but I can confirm that in 4.27, with that resolution, something very strange happens.
Unless you have a plugin in 4.27, and you’re not part of one of those trendy sects that hate Unreal 5, I would recommend moving to 5.4 or 5.5.