Thanks for your reply and your suggestion. I implemented those steps and it’s given me another error seemingly related to C compilers - it’s also given me an update log. Any ideas?
Depending on your platform, PETSc may take an hour or more to build!
Traceback (most recent call last):
  File "/Users/os3918/Documents/firedrake/src/../bin/firedrake-update", line 1766, in <module>
    install("petsc/")
  File "/Users/os3918/Documents/firedrake/src/../bin/firedrake-update", line 882, in install
    build_and_install_petsc()
  File "/Users/os3918/Documents/firedrake/src/../bin/firedrake-update", line 1017, in build_and_install_petsc
    check_call([python, "./configure", "PETSC_DIR={}".format(petsc_dir), "PETSC_ARCH={}".format(petsc_arch)] + petsc_options)
  File "/Users/os3918/Documents/firedrake/src/../bin/firedrake-update", line 539, in check_call
    log.debug(subprocess.check_output(arguments, stderr=subprocess.STDOUT, env=os.environ).decode())
  File "/usr/local/Cellar/python@3.9/3.9.9/Frameworks/Python.framework/Versions/3.9/lib/python3.9/subprocess.py", line 424, in check_output
    return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
  File "/usr/local/Cellar/python@3.9/3.9.9/Frameworks/Python.framework/Versions/3.9/lib/python3.9/subprocess.py", line 528, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '['/Users/os3918/Documents/firedrake/bin/python', './configure', 'PETSC_DIR=/Users/os3918/Documents/firedrake/src/petsc', 'PETSC_ARCH=default', '--download-hwloc',
 '--download-superlu_dist', '--download-hdf5', '--download-mpich', '--download-mpich-configure-arguments=--disable-opencl', '--with-fortran-bindings=0', '--with-x=0', '--download-chaco', '--download-pastix', '--with-cxx-dialect=C++11', '--CFLAGS=-I/usr/local/opt/openblas/include
 -Wno-implicit-function-declaration', '--with-zlib', '--download-metis', '--download-eigen=/Users/os3918/Documents/firedrake/src/eigen-3.3.3.tgz ', '--LDFLAGS=-Wl,-rpath,/usr/local/opt/openblas/lib -L/usr/local/opt/openblas/lib -L/usr/local/opt/gcc/lib/gcc/8',
 '--download-hypre', '--with-debugging=0', '--download-hwloc-configure-arguments=--disable-opencl', '--download-netcdf', '--download-scalapack', '--with-c2html=0', '--download-ptscotch', '--with-shared-libraries=1', '--download-mumps', '--download-pnetcdf',
 '--download-suitesparse', '--with-blaslapack-dir=/usr/local/opt/openblas', '--download-ml']' returned non-zero exit status 1.
Update log saved in /Users/os3918/Documents/firedrake/firedrake-update.log