Development setup, best way to do this, please advice?

I’m developing/running an application first on a PC/MacBook before putting it onto the Arduino. This is faster, it is easier for debugging. compared to each time download the application to the Arduino.

How can I connect the debugger in the Nextion IDE to the program running on the PC/MacBook? Should I use two serial ports and connect them to each other?

So the application on the PC/MacBook sends commands via the serial port to the 2nd serial port to which the debug Nextion application is connected?

The Nextion libraries provided are for the Arduino env. Could they also be used in a PC/MacBook command line application?

Is this the way to solve it? Or is there a different method?

Again, building a new application from scratch on a PC and easy/fast debug environment is easier and faster compared to each time downloading a slightly modified app into the Arduino.

That is a great way to handle this and UN user @hag has made a rad tool which does just that.

You can buy a TTL/5V cable for the USB port on your computer. Look this up on amazon:

FTDI Chip USB to 5v TTL UART Serial Cable 6 Way 0.1" Pitch Terminated Connector 5.0V Signalling Converter Adapter Cable 6FT Compatible TTL-232R-5V. There are several options, they are all around $15.

You will have pins for RX, TX, and Com. There will be other pins, but you won’t need them. Wire these to your arduino port (RX goes to TX, and vice versa). If you make sure your baud rates are matching you should be fine.

When you go to debug, there will be a box at the bottom of the screen for User MCU input. Once you click on that, you will see a couple boxes for baud rate and com channel. If you don’t know your com channel, you will have to go to your device manager and find it.

Good luck.