I recently purchased a LePotato which is readily available compared to the Raspberry Pi but based off the AML-S905X-CC chip. It isn't as fast as a Raspberry Pi 4 but works well enough. I got it up and running Armbian on a SD card fairly quickly.
You can find a spreadsheet online explaining the header pinouts. But I could not find any good diagrams showing what pins had what function. So I decided to make some for myself.
The following images were made by processing the spreadsheet. Each one is an SVG so you can scale it up as much as you need. On the left and right of the image are the references so you can orient the board the same way when looking at the header.