Vortex Sound Research

There may be a better sub for this but it seems lots of people on here are accomplishing this somehow.

I’m looking to record a stereo line in to my iPhone 11 Pro without using some additional expensive interface. I’ve found that using a TRS to TRRS adaptor I could probably trick it into recording mono over the “headset mic” input, but I’m trying to find a way for a stereo line in. Even most iOS interfaces are meant for mono inputs, so what’s my best option here for something quick and easy? Are most people recording audio and video separately and then syncing it up?

Thanks!