Anyone know if there is an actual setting in the DJI GO4 APP for the 8GB Internal memory storage.  My maiden flight today with my Mavic Air and I received the error that the Internal 8GB was full.  It asked me if I wanted to switch to my micro-SD card.  I said 'Yes'.  This appears to be the default setting but wondering where that setting is found.

I am guessing that perhaps you can click on the Memory Card here.  Didn't get a chance to test.  Wondering if anyone can confirm yet.   I'm running the newest firmware that just got released today (02/09/2018).

I have Mavic Pro, so I presume it should work similarly.

There is a video cache in the phone, which you can set the limit, if you set "Auto", it will use all available free storage in your phone.  This is for the storage of the 720p video transmitted back to your phone as it flies.

The full resolution image ( resolution as defined by your video setting, 4K, 2.7 K etc. ) is stored in the SD card on the drone, limited by the size of the SD card.
I think the "20GB" indicator is for the size available on your on-drone SD card. if you touch it, it'll probably changes to "video time left", which probably is more easy to understand, so you can tell how much video record time you have left, in terms of space available on the SD card.