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)
If retroarch is too much you can try Lemuroid. Lemuroid is a much simpler emulation app with a more straightforward GUI. It doesn’t come anywhere near the features or number of cores of retroarch but it supports most common retro systems.