After the following fix, the tester app goes from saying unsupported to this lovely screen!
And away we go!
*To follow this guide you need to install MT Manager :
https://mt.jouyo.cn/MT2.9.0-3.apk
*Also, this (or similar) app to test if it is enabled:
https://play.google.com/store/apps/d...toothhidtester
1 Open MT Manager, and give it root permissions. Then navigate to Vendor/Overlay/BluetoothResCommon.apk
2 Open the apk with VIEW function and open resources.arsc with the included arsc editor
3 Open resources.arsc, then com.android.bluetooth.overlay.common, then bool, and then bool once more.
4 Change Profile Supported Hid Device to true.
5 Save changes, then make sure permissions are rw-r-r (mine were by default)
6 Reboot the RP2
7 Open tester app, and test for support.
8 Profit.
(This thread here gave me the idea and a starting place, but I needed to change something in a different location.)
https://forum.xda-developers.com/redmi-note-7/how-to/enable-bluetooth-hid-profile-t4071767/amp/
I've included a link to original thread in case you want to read the original without my changes)
Hope this helps anyone.
-Cheers