Hello, are you using a widescreen patch for the game? Its possible the one you’re using was made for the CD copies of the game [such as the one designed for Pharaoh without Cleopatra]. If you’re using the one created by Crudelios (i won’t post a link here, but it can be easily found via google search or on the description of youtube videos by gamerzakh), then this shouldn’t be happening, as the Crudelios patch is designed for the drm-free digital copies.

Failing that, i would just use the Verify Game Integrity option on the game entry in the Steam Desktop app, in case any files have been changed. Alternative,y, you could try uninstalling and reinstalling the game, but take a backup of any save games that you have, as they’ll probably be erased.