To get the sniffer and firmware files, run the bootstrap subcommand:
nrfutil ble-sniffer bootstrap
This makes nRF Sniffer for Bluetooth LE runnable from Wireshark by copying a shim executable to Wireshark's external capture (extcap) directory.
The command also installs the nRF Logger for Bluetooth Host Controller Interface (HCI) plugin.
To install only one of the two plugins, and remove the other if it is already installed, use the --only option with ble or hci, for example nrfutil ble-sniffer bootstrap --only ble.
You can now use nRF Sniffer for Bluetooth LE from Wireshark. See Running nRF Sniffer for more information.