Did a search on this and found some post from a few years ago, but no solutions.
Picked up a Apple Lightning Digital AV Adapter to use with an iPhone XR or SE 2020 and my Optoma HD143X.
When I try and play .mkv files (1080p Blu Ray rips with MakeMKV) with either Infuse Pro 5.9.6 or 6.5.2 playback drops frames and stutters constantly. This happens with every file whether or not it is streamed or downloaded to the iPhone. No issues playing back on the phone itself or on an Apple TV HD or 4K. None Infuse playback via the Lightning Digital AV Adapter is also fine.