Digital Elevation Models (DEM file) restrictions

G’day,

What is the resolution that the DEM files that one can upload ? I’m operating in switzerland, and our government provides (free) a 0.5 m horizontal resulution height model of Switzerland that includes buildings and vegetation (but no power lines or poles).
off course it uses the swiss coordinate system so it requires some reprojection and likely also some resampling.
But what resolution (or file size) can litchi handle on an iPhone?
I need to fly low, and in mountainous terrains to hunt for invasive plants, so a high resolution model is important.
Any info is welcome. Cheers