A: The encode may have letterboxing inside 1280×720. Use VLC → Crop → 2.39:1 or set aspect ratio manually.
MKV Video: x265 10-bit, 1280×536, 5 Mbps, CRF 20 Audio: AC3 5.1 @ 640 kbps (compatibility) + DTS 5.1 (optional) Subtitles: English PGS The Batman -2022- -720p- -BluRay-
If you have decided on 720p for The Batman (2022), target this specific profile: A: The encode may have letterboxing inside 1280×720