main.c

// Include the most common headers from the C standard library
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// Include the main libnx system header, for Switch development
#include <switch.h>

#define MAX_DEVICES 20

// See also libnx pad.h / hid.h.
void print_hex(char* data[], int length) {
    for (int i = 0; i < length; i++) {
        printf("%02x ", data[i]);
    }
}

// Main program entrypoint
int main(int argc, char* argv[])
{
    // This example uses a text console, as a simple way to output text to the screen.
    // If you want to write a software-rendered graphics application,
    //   take a look at the graphics/simplegfx example, which uses the libnx Framebuffer API instead.
    // If on the other hand you want to write an OpenGL based application,
    //   take a look at the graphics/opengl set of examples, which uses EGL instead.
    consoleInit(NULL);
    setInitialize();
    setsysInitialize();

    // Configure our supported input layout: a single player with standard controller styles
    padConfigureInput(1, HidNpadStyleSet_NpadStandard);

    PadState pad;
    padInitializeDefault(&pad);
    SetSysBluetoothDevicesSettings settings[MAX_DEVICES];
    s32 total_out;


    printf("\x1b[1;1HPress PLUS to exit.");
    printf("\x1b[2;1H");

    int line = 4;
    Result rc = setsysGetBluetoothDevicesSettings(&total_out, &settings, MAX_DEVICES);
    if (R_SUCCEEDED(rc)) {
        for (int i = 0; i < total_out; i++)
        {
            SetSysBluetoothDevicesSettings *device = &settings[i];
            if (device->addr.address) {
                printf("\x1b[%d;1HName: %s %d:%d %x btAddr: ", line, device->name2, device->vid, device->pid, device->sub_class);
                for (int i = 0; i < 6; i++) {
                    printf("%02x ", device->addr.address[i]);
                }
                line++;
                printf("\x1b[%d;1H Type: %d  Key: ", line, device->key_type);
                for (int i = 0; i < 16; i++) {
                    printf("%02x ", device->link_key[i]);
                }
                line++;
            }
        }
            
            // Print link key etc
    }
    // Main loop
    while(appletMainLoop())
    {
        // Scan the gamepad. This should be done once for each frame
        padUpdate(&pad);
        // padGetButtonsDown returns the set of buttons that have been
        // newly pressed in this frame compared to the previous one
        u64 kDown = padGetButtonsDown(&pad);
        // padGetButtons returns the set of buttons that are currently pressed
        if (kDown & HidNpadButton_Plus)
            break; // break in order to return to hbmenu
        // Update the console, sending a new frame to the display
        consoleUpdate(NULL);
    }

    // Deinitialize and clean up resources used by the console (important!)
    consoleExit(NULL);
    return 0;
}

setsysGetBluetoothDevicesSettings(&total_out, &settings, i);

You shouldn't call this in a loop, but instead define an array of SetSysBluetoothDevicesSettings to receive the entries and then loop on the output. From firmware 13.0.0+ the database can contain up to 20 entries. Prior to that it was 10.

Something like

#define MAX_DEVICES 20

SetSysBluetoothDevicesSettings settings[MAX_DEVICES];

s32 total_out;
Result rc = setsysGetBluetoothDevicesSettings(&total_out, settings, MAX_DEVICES);
if (R_SUCCEEDED(rc)) {
    for (int i = 0; i < total_out; ++i) {
        SetSysBluetoothDevicesSettings *device = &settings[i];
        
        // Print link key etc
    }
}

printf("%d ", settings.link_key[j]);

Also, you probably want to use %02x here instead of %d to print the bytes in hex, as this is likely more useful for whatever follows.

thanks for the comments, it wasnt really clear from the defenition to me and I'm not really a c guy :)