The most effective way to achieve this is via the True Mirror FOV mod on Steam Workshop . :
: Older manual methods involved editing truck .sii files to change mirror_fov values (e.g., setting a close mirror to 24.0f for a narrow, realistic zoom). Recommended Realistic Setup True Mirror FOV for ETS2 1.47
For the most immersive experience, pair your mirror FOV with these interior settings: The most effective way to achieve this is
: Open the console (~ key) and enter g_phys_mirrors 1 to enable the physically simulated mirror system. True Mirror FOV for ETS2 1.47