one moment !!!! Sorry but when I wrote Serial.Available I was intending myBluetooth.Available()
If it works only if you remove the curly braces, this means that your loop() is not waiting far a character from the Serial line and processes always an old character, irrespective of what is received, or not, on the serial line !!!
Anyway, if restoring the correct istruction myBluetooth.Available() and by putting the curly braces it does not work, this means that the Arduino board is never receiving from the BT any character.
Let's try differently: the annexed .aia is an app that I developed few days ago.
It drives an Arduino (Nano, but it is irrelevant for your purposes) fitted with a BT HC05 to manage an RGB LED's strip on my car.
The app sends several "one character" commands via BT to my Arduino board that drives the RGB's.
The Arduino board does not send back any feedback to the app, but it just receives. Most probably this is sufficient also for your needs. The app also sends periodically a "live" character to the HC05, just to avoid the the BT disconnects itself if not solicitated for a long time.
The "true commands" are sent only whenever a button is pressed (the app runs on my phone).
In the .aia file, it is also included the .ino program that you can find in the "asset" directory (you open the .aia with winzip or 7zip so you can extract the .ino).
Please don't mind if the comments are in Italian. The code is quite simple, but if you need an english translation, please let me know.
Hoping this truly helps you
RGB_BT.aia (352.2 KB)
PS in the app you will see that there are two close app paths: one is suitable for Android versions capable to handle the android.bluetooth.adapter.action.REQUEST_DISABLE activity, and the other path for those older Android versions not featuring this activity.
And, if the Android version is one of those where the activity is executed, in order to leave time do accomplish the activity, before affectively closing the app, I start a timer that allows some seconds before closing really the app, otherwise the activity is not done, because the app closes too early.