Two versions of a mini monitor

A version using a Arduino and a Midi shield (Yellow wires are for display)
D0 (RX) is used for the Midi IN signal.

Above a Teensy 4.0 version. This one uses MIDI over USB.

Next to add: Rotary encoders, to select a CC Channel and display values graphically

CODE for Teensy version

#include <U8g2lib.h>
#include <Wire.h>
#include <MIDIUSB.h>   // Teensy's built-in USB MIDI

// SH1106 128x64 I2C constructor
U8G2_SH1106_128X64_NONAME_F_HW_I2C u8g2(U8G2_R0, /* reset=*/ U8X8_PIN_NONE);

void setup() {
  u8g2.begin();
  u8g2.clearBuffer();
  u8g2.setFont(u8g2_font_6x12_tf);
  u8g2.drawStr(0,12,"MIDI Monitor Ready");
  u8g2.sendBuffer();
}

void loop() {
  // Check for incoming MIDI

  while (usbMIDI.read()) {
  u8g2.clearBuffer();
  u8g2.setFont(u8g2_font_6x12_tf);
  u8g2.drawStr(0,12,"MIDI Monitor Ready");
  u8g2.sendBuffer();
    byte type = usbMIDI.getType();
    byte channel = usbMIDI.getChannel();
    byte data1 = usbMIDI.getData1();
    byte data2 = usbMIDI.getData2();

    int y = 24;

    if (type == usbMIDI.NoteOn && data2 > 0) {
      u8g2.setCursor(0, y);      u8g2.print("Note ON     "); // pad
      u8g2.setCursor(0, y+12);   u8g2.printf("Ch:%-3d", channel);  // pad width 3
      u8g2.setCursor(0, y+24);   u8g2.printf("Note:%-3d", data1);
      u8g2.setCursor(0, y+36);   u8g2.printf("Vel:%-3d", data2);
    } 
    else if (type == usbMIDI.NoteOff || (type == usbMIDI.NoteOn && data2 == 0)) {
      u8g2.setCursor(0, y);      u8g2.print("Note OFF    "); // pad
      u8g2.setCursor(0, y+12);   u8g2.printf("Ch:%-3d", channel);
      u8g2.setCursor(0, y+24);   u8g2.printf("Note:%-3d", data1);
    } 
    else if (type == usbMIDI.ControlChange) {
      u8g2.setCursor(0, y);      u8g2.print("Control Chg ");
      u8g2.setCursor(0, y+12);   u8g2.printf("Ch:%-3d", channel);
      u8g2.setCursor(0, y+24);   u8g2.printf("CC#:%-3d", data1);
      u8g2.setCursor(0, y+36);   u8g2.printf("Val:%-3d", data2);
    } 
    else {
      u8g2.setCursor(0, y);      u8g2.print("Other MIDI  ");
      u8g2.setCursor(0, y+12);   u8g2.printf("Type:%-3d", type);
    }

    u8g2.sendBuffer();
  }
}

CODE for Arduino plus shield

#include <U8g2lib.h>
#include <Wire.h>
#include <MIDI.h>   // FortySevenEffects MIDI library

// SH1106 128x64 I2C (page buffer, low RAM)
U8G2_SH1106_128X64_NONAME_1_HW_I2C u8g2(U8G2_R0, /* reset=*/ U8X8_PIN_NONE);

// MIDI on hardware Serial (RX=D0)
MIDI_CREATE_INSTANCE(HardwareSerial, Serial, MIDI);

char line[12];  // small buffer for formatting

void setup() {
  u8g2.begin();
  u8g2.setFont(u8g2_font_6x12_tf); // proportional font, small size

  // Initial message
  u8g2.firstPage();
  do {
    u8g2.setCursor(0, 12);
    u8g2.print("MIDI Monitor Ready");
  } while (u8g2.nextPage());

  MIDI.begin(MIDI_CHANNEL_OMNI);  // listen to all channels
}

void loop() {
  if (MIDI.read()) {
    byte type    = MIDI.getType();
    byte channel = MIDI.getChannel();
    byte data1   = MIDI.getData1();
    byte data2   = MIDI.getData2();

    // Page buffer redraw
    u8g2.firstPage();
    do {
      // Title
      u8g2.setCursor(0, 12);
      u8g2.print("MIDI Monitor");

      int y = 24; // start lower down

      if (type == midi::NoteOn && data2 > 0) {
        u8g2.setCursor(0, y);      
        u8g2.print("Note ON   ");

        snprintf(line, sizeof(line), "Ch:%-3d", channel);
        u8g2.setCursor(0, y+12);   u8g2.print(line);32

        snprintf(line, sizeof(line), "Note:%-3d", data1);
        u8g2.setCursor(0, y+24);   u8g2.print(line);

        snprintf(line, sizeof(line), "Vel:%-3d", data2);
        u8g2.setCursor(0, y+36);   u8g2.print(line);
      } 
      else if (type == midi::NoteOff || (type == midi::NoteOn && data2 == 0)) {
        u8g2.setCursor(0, y);      
        u8g2.print("Note OFF  ");

        snprintf(line, sizeof(line), "Ch:%-3d", channel);
        u8g2.setCursor(0, y+12);   u8g2.print(line);

        snprintf(line, sizeof(line), "Note:%-3d", data1);
        u8g2.setCursor(0, y+24);   u8g2.print(line);
      } 
      else if (type == midi::ControlChange) {
        u8g2.setCursor(0, y);      
        u8g2.print("Control Chg");

        snprintf(line, sizeof(line), "Ch:%-3d", channel);
        u8g2.setCursor(0, y+12);   u8g2.print(line);

        snprintf(line, sizeof(line), "CC#:%-3d", data1);
        u8g2.setCursor(0, y+24);   u8g2.print(line);

        snprintf(line, sizeof(line), "Val:%-3d", data2);
        u8g2.setCursor(0, y+36);   u8g2.print(line);
      } 
      else {
        u8g2.setCursor(0, y);      
        u8g2.print("Other MIDI");

        snprintf(line, sizeof(line), "Type:%-3d", type);
        u8g2.setCursor(0, y+12);   u8g2.print(line);
      }
    } while (u8g2.nextPage());
  }
}