are those cinematic black bars in the renders?
I render at an aspect ratio of 2.40:1, which is 3840x1600, and then in Photoshop I extend the frame to 16:9, which is 3840x2160 by using black PNG overlays.
I used to render in 16:9 and add the bars over the top, to allow me to reframe stuff if I needed to because of the extra real estate at the top/bottom of the image, but it would take longer to render and it was unnecessary if I just bothered framing stuff properly in the first place lol