Why? What dictates the choice of the Nucleo board and the rather ancient RFM95 module?
Rather than struggle with less optimal hardware, can you use a Semtech SX126X board - this will allow you to run the soon to be deprecated LoRaMac-node and it’s replacement, LoRa Basic Modem.
Or even do you have to use the Nucleo - there are many other boards around running a variety of LW stacks.