iOS desktop-forward renderer

When I select both renderer options for iOS the game runs nicely on older devices but appears to crush on lunch on newer devices, which appears to me that there is a problem with desktop forward renderer. Therefore I am wondering if anybody has been able to use both renderer option without any problems. The game is fine with ES 3.1 on android. It would be a huge performance gap if I cannot use ES 3.1 on iOS.

Does anybody know if it would help to use higher Metal version? Would this resolve the problem of crushing on start?
Sorry for asking these questions instead of trying as I only have an iPhone 5s and it plays fine on that but does not seem to work properly in higher devices so I am guessing it must be because of desktop forward renderer that only kicks in on newer devices.

Using Metal v2.1 that is used on iOS 12 resolved this issue.

You can change mobile/desktop render for difference devices?