Move arial_black_16.h into your Arduino sketch folder (or the src folder of your PlatformIO project).
At first glance, this looks like a typo or a corrupted file path. But to those working with low-level graphics libraries (like U8g2, Adafruit_GFX, or LVGL on constrained devices), this string represents a holy grail: a pre-rendered, monospaced, bitmapped font file for the Arial Black typeface at a 16-pixel size. arial black 16.h library
void setup() { u8g2.begin(); u8g2.setFont(arial_black_16); // Note: The variable name inside your .h file } Move arial_black_16
This brings us to a specific, often misunderstood search term: . or LVGL on constrained devices)
#include <U8g2lib.h> // Use the reference to the external font U8G2_SSD1306_128X64_NONAME_1_HW_I2C u8g2(U8G2_R0, U8X8_PIN_NONE);