The micros USB port on the back of the Fire TV Cube will most commonly be used to connect the Ethernet Adapter that comes included in the box with every Fire TV Cube, but with the right adapters or accessories, it can be used for so much more, as is described in this article.
What is the difference between OTG cable, OTG adapter and OTG card
This Micro USB to USB OTG cable supports OTG (On-The-Go) function. This cable fits for smartphone to connect with other USB device such as USB flash driver, game controller keyboard, or use for extension usage.
Unitek OTG USB 2.0 AF Cable to Micro USB BM (Y-C438GBK)
USB C OTG adapter
Micro USB to Micro USB OTG Cable - 10-12 / 25-30cm long : ID 3610
This Micro USB to USB OTG cable supports OTG (On-The-Go) function. This cable fits for smartphone to connect with other USB device such as USB flash driver, game controller keyboard, or use for extension usage.
Unitek OTG USB 2.0 AF Cable to Micro USB BM (Y-C438GBK)
USB 2.0 Cable OTG A F Micro USB M with USB 30cm Black - USB Cables
Rocstor Premium USB Adapter for Tablet, PC, Mouse, Cellular Phone , Keyboard, Digital Text Reader - 1 Pack - 1 x Micro USB Type B Male - 1 x USB Type
Micro USB to USB Type-A Adapter - M/F - On-The-Go (OTG) Convertor
The different Micro USB OTG Adapters and Accessories that work
Huion OTG Adapter adapter for Android Devices.