Hello,
I’m using TFT_eSPI library downloaded in Arduino IDE with the library manager. It is working and compiling fine. It is one of the most popular display library and I did not modify it.
The file I wanted to debug located in /Extensions folder and it is included as “Extensions/Smooth_font.cpp”
So the Arduino can include files from sub folders..
This looks like a bug from in your IDE. Since, like I mentioned, the Header File virtual folder has all the sub folders of the project.