This is how I upgraded my realme 4K Smart Google TV stick from 8GB ROM to 24 GB by using an external USB Drive flash disk. This tutorial also works on Xiaomi’s Mi TV Stick as well as on the Amazon Firestick.
To increase the storage, you need to get a USB OTG cable with power and connect your USB drive. In the settings you need to erase and format it as device storage.
Watch the simple tutorial video below.
Alternative Cable Names
Mini Micro USB OTG Adapter Host Power Y Splitter USB to Micro 5 Pin Male Female Cable for Fire Stick Android Phone Accessories USB Type A Female to Micro USB Male Host OTG with Micro USB Female Y Cable External Power Supply for Mobile Phones and Tablets