When exporting a texture atlas as PNG, the issue of the filename appending .atlas.txt can occur if the extension is not correctly set in the export settings. To resolve this, ensure that the "Output file" property is set without the .atlas.txt extension. You can specify the output path as your/output/dir/name without any extension, and the correct extension will be appended automatically. If the extension is set to .atlas.txt in the settings, it will append this to the filename, resulting in output.atlas.txt.png. Adjusting the settings to remove the .atlas.txt extension should fix the issue.
