First Press ALT+R (to open the radeon control panel)first go to settings (the nut icon near the top right of the screen) then in the sub tabs go to
DISPLAY (the 3rd sub tab from the left) then just below the FREESYNC option there would be a option to enable VIRTUAL SUPER RESOLUTION enable it then wait a few seconds then go on your custom resolution then press the delete option it should delete then. then disable the VIRTUAL SUPER RESOLUTION and you are good to go. take a deep breath and promise you will never mess with the setting ever again.
If its not working then idk accept the reality and move on ( btw i dont trust myself with reinstalling drivers) or just buy a new hardrive and restart with a new fresh life.
btw all credits go to
Had this same issue even in the newest 21.4.1 version; I was able to finally delete the custom resolution by changing mode from from the Display settings > Advanced display settings > Display adapter properties > List All Modes, as described by xoker01 on the first page.
Just changing display resolution the basic way didn't work. Factory-resetting AMD Software didn't work; the custom resolution persisted even though the reset. Turning Virtual super resolution on and off didn't work either.