You can try downloading and sideloading the Amazon AppStore build: Plex for Android - #495 by PlexAndroidReleaser
However, it may not work if your phone is running Android 13 and definitely won’t work if running Android 14.
The Plex Android mobile & Android TV apps are 32-bit apps (armv7a is a 32 bit architecture).
The Pixel 7a has a 64-bit CPU. It runs either Android 13 or 14. Android 14 does not support 32-bit apps. I could not find any definitive info if a Pixel 7a running Android 13 will run 32-bit apps.
The Pixel 5 is old enough that it still supports 32-bit apps.
Note that sideloaded apps do not auto update. You will have to manually update as future versions are released. Also, you’ll be using the app in an unsupported method.
TBH, your best alternative is to switch to the Google Play store and pay the unlock fee.
