Trying to install nrfutil on a system with Python 3.9 but it only installs the old version 5.2.0 which is broken on Python 3. This is the last version before the version check was introduced in setup.py.
pip install --user nrfutil
It's possible to install nrfutil 6.1.0 with --ignore-requires-python however the pc_ble_driver_py dependency fails.
Unfortunately, the pc_ble_driver_py dependency does not appear to be compatible with the Python 3.9 release yet. Same issue was reported by another forum user a few days ago (link). While waiting for this to be resolved I'd suggest you use the compiled executables available at https://github.com/NordicSemiconductor/pc-nrfutil/releases or downgrade to Python 3.8.