2 blinks of the LED indicate a "minor main board issue" according to Hysense.
Obviously, it is MAJOR until you find it.
Everything on the right side of that white hashed bar is the main board. Everything to the left is the PSU.
The blinking LED would indicate that the processor is working since it controls the LED and the sensors talk to it.
So, what could be MINOR? My first suspect would be diodes.
That large diode at the top probably supplies backlight voltage to those red and white wires.
However, with no video showing with a flashlight, it is probably not that. But it is easy to check.
The device below it should also be easy to test, but I can't tell what it is.
Next, try disconnecting all the connector cables and reconnecting them. That should cut thru any corrosion that might be on them.
There may also be some surface mount diodes, but I can't see them in your pictures.
There are a few transistors that you can test like the three to the right of the small black heat sink and a few on the bottom next to the composite inputs.
Other than that, you will have to remove the board for a much closer inspection, or just replace it.