Good afternoon!
Installed 4.020 via OTA - went without problems.
Capability of reboot from GUI is still missing.
This is still unfortunately true for reboot commands from terminal as well- so reboot is currently not possible - hard reset (power off) is neccessary.
BT remote is connected and initially doesn’t work correctly.
Have now installed BluetoothRemotePlugin and rescanned. GUI was for some reason tricky - it was not easily possible to get the found device selected but after several approaches some may strange combination kept the device selected in the drop-down and so a saving could be performed.
BT remote still doesn’t work properly, Volume up/down and skip back were missing as before.
The triggerhappy config file was moved or reflected to the externally visible INTERNAL storage Portion - nice idea.
Doesn’t work either initially - file belongs to root. Changing this it was possible to add the missing entries
KEY_VOLUMEUP 1 volumio volume plus
KEY_VOLUMEDOWN 1 volumio volume minus
KEY_PREVIOUSSONG 1 volumio previous
Restarting triggerhappy (possible from plugin-settings - great idea, as well!) and voilà: BT remote now works fine.
Thanks to @balbuze!
The poblem with one of the rotary encoders disappeared, both Rotary Encoders are doing their respective work.
(HW) Config:
Pi5,
Raspi 2 Display (DSI),
Two rotary encoders on several GPIOs - both working fine.
Working BT remote 
Testing:
Spotify plugin, works (my only use case).
Touch display (and corresponding plugin) works
“Now Playing” plugin works
Bluetoothremote plugin works! - BT remote is working (connected and signals detected)
Rotary encoders are working partly
WiFi is working (can access from laptop / phone).
CORRD link still only leads to app-store, no intergrations as far as I can see.
Many, many thanks for your effort. The result is awesome!
Warmest regards,
Ralf