You can use methods like File.AppendAllLines() in C# to add new data to an existing text file.

If you are working on a data logging project, I can provide: for writing data to files. Arduino code for logging sensor data to an SD card. Let me know what kind of data you are trying to save! Function to dump SD text files over serial - Arduino Forum

You can use json.dump() to serialize data and write it to a text file.

Cc Dumps.txt -

You can use methods like File.AppendAllLines() in C# to add new data to an existing text file.

If you are working on a data logging project, I can provide: for writing data to files. Arduino code for logging sensor data to an SD card. Let me know what kind of data you are trying to save! Function to dump SD text files over serial - Arduino Forum

You can use json.dump() to serialize data and write it to a text file.