Denon periodically releases firmware updates for the AVR-X520BT. Some recent updates have included:
Insert the USB memory device into the USB port on the front panel of the receiver. denon avrx520bt firmware update top
https://www.denon.com/en-us/product/av-receivers/avr-x520bt → Click “Downloads” → “Firmware” denon avrx520bt firmware update top
: Connect the USB drive directly to the unit; the receiver will not recognize devices connected through a USB hub. denon avrx520bt firmware update top
While not as comprehensive as the on-screen menu, the Denon Remote App (available for iOS/Android) can sometimes trigger an update notification.