I can install GNU Radio as described here and make it work with the Pluto SDR.
I can install gqrx as described here and make it work with the Pluto SDR.
However, the gqrx installation breaks the GNU Radio installation.
GNU Radio complains:
ImportError: No module named _iio_swig
What do I need to do to have both apps working?
You need to make sure the generated swig interface (_iio_swig) is on your python path. This is described in the installation instructions of your first link: https://wiki.analog.com/resources/tools-software/linux-software/gnuradio#compiling_the_gr-iio_blocks_for_your_pc