RX for serial does not work

As mentioned in this post

Some models of Arduino DUE boards have a problem with the RX for serial communication ! It works when communicating with the PC using the serial-USB. But it does not work when trying to communicate between two boards, for example.
I used the oscilloscope to measure the input signal in the RX pin (attached image) and the signal is cropped as soon i connect the TX signal from the source to the RX (DUE).

In this previous post, they came up with a very invasive solution to make it work, by including some resistor in the board.
My question is, can this problem be solved with some external resistor or any other component to be connected to some pin ?

To communicate thru Serial with another board, use RX1/TX1 or RX2/TX2, etc... but keep RX/TX for Serial PC monitor.

If the other board is not 3.3V compliant, add logic level shifters.