So for anyone who stumbles across this post, as of 2/8/2021 using FileOpenPicker with no other installed apps on the Hololens 2 doesn't work.
It took me forever to find this post but here's a partial answer
Open local data path with FileOpenPicker
So to make a TL;DR about that post. FileOpenPicker DOES work on Hololens, however, it works through externally installed File picker like OneDrive.
I don't know why I didn't find this post sooner until I went down every avenue to figure it out.
EDIT: I managed to solve my issue over on THIS POST if there is anyone stumbling across this issue hopefully that helps.
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