Like the previous FromSoftware Games, Elden Ring don’t support the ultra wide resolution too, but there is a simple fix thanks to the Flawless Widescreen application.
Flawless Widescreen is an application you can simply fix ultrawide problems of some games like Elden Ring.
How to Fix
After installing the Flawless Widescreen, you need to install the Elden Ring Plugin from the plugin section and check the checkboxes as you need.
Due to Easy Anti Cheat, there is a risk of ban for using this fix, so only use this fix in offline mode and remember to use it with your Own Risk!
Keep in mind that you need to keep the application running in order to game be fixed.
Besides ultrawide fix, you can fix FOV and 60 FPS Limit by this software.