[Steam Deck] Horizontal offset on Flycast when playing Metropolis Street Racer

Description

On Steam Deck, when playing Metropolis Street Racer on Flycast and using the widescreen cheat, the picture gets offset by (30-50?) pixels to the right. This causes part of the screen to be cut off. The VMU on screen is still displayed in the right place, it's just the game that's offset.

This doesn't happen on Windows 10, but the bug is still present when forcing the Steam Deck to use the Windows build through forcing the use of Proton.

Expected behavior

Windows and the Steam Deck to display the screen correctly centred

Actual behavior

Steps to reproduce the bug

1. Run Metropolis Street Racer (US) on Flycast on the Steam Deck with widescreen cheats turned on (and the widescreen hack disabled)

Bisect Results

This may have started around 1.15.0, although I can't roll back the version on Steam to check.

Version/Commit

You can find this information under Information/System Information

• RetroArch: 1.16.0

Environment information

• OS: Steam Deck Linux

Start by reproducing RetroArch 1.16.0 with Flycast, Metropolis Street Racer (US), and the widescreen cheat on Steam Deck Linux, with the widescreen hack disabled. Compare the result with Windows and with the Windows build through Proton to narrow down the platform-specific behavior. Done means the game image is centered without cutting off pixels while the on-screen VMU remains correctly positioned.