I found this in 4.17 release notes:
In preparation for officially dropping support for 32-bit applications and OpenGL on IOS, those options have been removed from the IOS Settings in the editor. They are currently still available in the ini configuration files, but the support will be deprecated in a future release.
But I didn’t find any mention of this in 4.18, or 4.19, or 4.20, meaning it is still available in the ini configuration files and support wasn’t deprecated yet??
I also read Apple is removing OPENGL support with iOS12.