currently can’t gain access to the SD Card storage when using the Android app on a Chromebook. Google has enabled the ability, but it requires updating the Android app to support the new storage protocols.
I do not officially support Chromebook 
But Yatse fully support SAF when sharing, so you can use any file browser on Chromebook and select share to have it played where you want.
I could do that. But was hoping to use the sync/download from Plex. 
Well that is a lot more complicated due to how shitty their interface is 
Can’t do what I want and will need to keep uri permissions and tons of shitty stuff.
Then face the 256 granted uri permissions limits and cry
Their solution is not ment for cache folders… The more things moves on, the less we can do things, because they think their usage covers all users needs.
So your best bet is to find a root tool that allows normal access to apps.
Yeah, I dug this up. It looks like Google is aware… But not making it a priority.
https://bugs.chromium.org/p/chromium/issues/detail?id=789045
I guess I’ll figure something else out for now.
Yep as more and more
Sorry but can’t do impossible things.