Hi there,
And Welcome Here…
Yes indeed there are, Starting with the Search over there on the top right. just try some of the keywords and you will get some great info about it. Sounds like you have experience , so Even the Examples included in the Arduino IDE are worthy of a look. The nrf52840 Xiao is the best starting point for this type project also, the documentation, LOW power consumption and ease of use will get you there in short order.
You can look to the Xiao sending Keyboard commands and keys in the HCI examples.
So you’ll connect buttons up to the Xiao, program it to Advertise as a peripheral, Connect to IT with a mobile phone and Will you subscribe to a characteristic or the button service char via BLE. any pressed buttons will be sent to the mobile. Does that sound close?
I have seen several examples of that sort of thing floating by here often, must be a homework assignment or something …LOL 
Have you looked at the Xiao WiKi ?
HTH
GL 
PJ 