When using armbian-config to select an overlay ("DTO001")e.g. for uart2, one is offered the full names w/ overlay prefix, e.g. sun7i-a20-uart2.
The system adds this to armbianEnv.txt: overlays=sun7i-a20-uart2
But it has also the line overlay_prefix=sun7i-a20
In the end, uart2 is not activated (no output from /dev/ttyS1) - after changing the overlay line to overlays=uart2, I can read from /dev/ttyS1.
System is Armbian 25.2.2 stable (bookeworm), Armbian Linux 6.12.20-current-sunxi.