Z9X Pro: which apk's to install "armv7" or "armv8"? 64bit or 32bit?

Stupid newbie-question - but the manual doesn't elaborate on that issue either:

Which type of 3rd-party-apk's need to be downloaded for installation on the Z9X Pro?

From my initial experiences it would seem that "armv7"-64bit is the way to go. Am I correct in that assumption?

And a second question - since my first post concerning that topic has remained unanswered for more than a week by now: Does anyone see the following important system-files-apk installed on his system (or has managed to install himself)? If so - how has it been introduced to your system?
App-Name within Android: "FILES"
Package-name: "com.android.documentsUI"

Any help would be appreciated.

 

these pro series run on android tv os so sadly most android apps wont work
ie
USB Audio player pro ..even the android tv mod version wont work

 

When I download my Neutron Music Player, I use "Neutron Music Player (ARMv7+NEON)". It installed and worked well on my Z2600.

 

So the situation concerning 3rd-party-apps doesn't seem all that bad, it would appear. This pretty much chimes with my personal experience with the Z9X-Pro so far. I've managed to install more than a dozen of essential apps by now, most importantly file-managers, browsers Opera and Firefox and proven VLC-media-player, meanwhile also available for Android.

It is only that damn download-problem that stubbornly persists. In order to access ample download-space I had to set the standard-storage-location for these apps to my attached USB-drive - yet unfortunately in vain. It is a known limitation for recent Android-versions (I believe from v.9 on but could be wrong about that) that they cannot directly access storage-space on any USB-drive but can do so indirectly using the System-app "FILES" as is the case on all my Android-tablets.

The best Android-File-Manager that I know of (Total_Commander_for_Android) even says so explicitly when write-access to the USB-storage is required. While TC_A can read the USB-storage it will complain whenever copying, movig or deleting files on the USB-drive is required, that TC_A can only indirectly gain access there via calling the FILES-system-app and granting TC_A access from there. But then nothing will happen - as no FILES-app is available on the Z9X.

Does anyone know if for (as it seems dastardly leaned-down) Android-TV-OS there is any other proper way to access (my own, not Google's, not Zidoo's) USB-storage-space? Can the Z9X even be rooted via Magisk? But that would presumably require the possession of a proper boot-image. So where to get that from and how to boot the Z9X into recovery-mode?