suggest or state that: 3. A list will now appear of all available cores. Now let's say we are using an Nano 33 BLE board, and we want to install the core. Simply enter the name in the search field, and the right core (Mbed OS Nano) will appear, where the Nano 33 BLE features in the description. Click on the "INSTALL" button.
The "Arduino Mbed OS Nano Boards" platform contains a script that is intended to create a udev rules file that configures the file permissions that will be required for Arduino IDE to be able to upload to the serial port of the Nano 33 BLE Sense.
However, the creation of that udev rules file can only be done when running as a superuser (e.g., as the root user). Since the user probably isn't (and certainly shouldn't be) running Arduino IDE as superuser, it was pointless for the developers to add that script but they did it anyway. The script is configured to check whether it has the necessary permissions. If not, it prints that ridiculously vague "Please run as root" message you noticed.
You can run the script directly from the Linux terminal as superuser in order to create the udev rules file. There are instructions for doing that here:
Connect your Nano 33 BLE board to your computer with a USB cable.
Select File > New Sketch from the Arduino IDE menus.
Select the board and port from the Arduino IDE menus.
Select Sketch > Upload from the Arduino IDE menus.
Wait for the upload process to finish.
If the upload was successful, then everything is already configured as needed with the port and you can forget all about that "Please run as root" message and the script.
If there is an error when you attempt the upload, then you will know that you need to run the script.