Suggestion to use a switch in the circuit

[paulskirk53]

I have used the circuit here which is a simple modification to the pymcuprog UPDI diagram. You can use an FTDI device as a programming conduit as well as a serial comms device. I've tested this on my AVR4809. Do serial comms in one switch position and program the chip using pymcuprog in the other position. Hope it helps.