There is a PR in Adadruit_CircuitPython_RFM that fixes a known issue with Spreading Factor = 6

Should this also be implemented here?
It will increase the size of the library and further impact the smaller M0 build (feather M0 rfm9x)?

Users who need SF=6 can use the Adafruit_CircuitPython_RFM library but that will not run on the small M0 boards.

SF=6 is not supported by the RadioHead Arduino library so without it, the adafruit_rfm9x library is still "compatible" with Radiohead ;-)

I don't know how much it will increase the library - likely a few 10s of bytes.

How you would like to proceed?