Download the necessary files below (links to XDA Threads).
In a world driven by planned obsolescence, flashing a custom ROM is an act of rebellion. It is a refusal to accept that a piece of hardware containing rare earth metals and perfectly functional glass is useless just because the manufacturer stopped sending packets of data to it. Asus Zenpad 10 Z300c Custom Rom
Do not fall for fake "Android 10 GSI" videos on YouTube for the Z300C. They either do not boot or have broken hardware acceleration. Download the necessary files below (links to XDA Threads)
/e/ is a de-Googled ROM that uses MicroG. It is perfect if you want to use the Zenpad without sending data to Google. Do not fall for fake "Android 10 GSI"
Attempting a full AOSP or LineageOS build will likely result in a bricked device due to Intel SoFIA's closed-source drivers.