I installed Ignited via SideStore. No Jailbreaking necessary. Not computer tether. SideStore can renew the side loaded emulator every 7 days when on WiFi. The iPhone is perfect for DS emulation with a stylus.
(Ignited is a fork of Delta with more options, and SideStore is a fork of AltStore, with no computer tether needed)
I don’t know how it works in RetroArch, with Delta/Ignited you can change the skin which also manages the size and position of the screens. I even designed custom skins to play full screen with no controls with Zelda since you don’t need the abxy and arrow buttons to play.