I can assume that this is a rectangle marked in yellow (but this is only a guess and probably not correct, be careful). For UART, a 4-pin connector is typically used (which uses only 3 pins). In the photo (yellow rectangle) two rows of 4 contacts. I don't know which of the contact rows to refer to UART. Show a photo of the entire Board at the top to try to find labels that describe the purpose of the connectors. Typically, the first 3 contacts are used in the UART connector (the count is from the square contact). The square pin is the ground, the two internal pins are Rx and Tx (or Vice versa Tx and Rx). If you connect and configure and there is no output to the screen in the UART console, you can try to swap the connection to Tx and Rx.
Can you show the UART log of the last Armbian image?