The project file refers to "main.tscn" and main.tscn refers to "main.gd". But the respective files are named "Main.tscn" and "Main.gd". This probably works in Windows where filenames aren't case sensitive, but it doesn't work on Linux. I suggest either renaming the files to all lower case, or changing project.godot and main.tscn to refer to "Main.tscn" and "Main.gd" respectively.
The project file refers to "main.tscn" and main.tscn refers to "main.gd". But the respective files are named "Main.tscn" and "Main.gd". This probably works in Windows where filenames aren't case sensitive, but it doesn't work on Linux. I suggest either renaming the files to all lower case, or changing project.godot and main.tscn to refer to "Main.tscn" and "Main.gd" respectively.