You are using a feature from Scratch 3.0+ that doesn't exist, or the JSON syntax is broken. Fix: Validate your JSON using a linter (like JSONLint). If you modified the code manually, one missing comma will crash the entire parser.
Before understanding the converter, you have to understand the container. Since Scratch 3.0 launched in 2019, project files have carried the .sb3 extension. But unlike the old .sb or .sb2 binary formats, the SB3 is a wolf in sheep’s clothing. Zip To Sb3 Converter
Use this if your file is called project.zip but you know it should be a Scratch project. You are using a feature from Scratch 3
An SB3 file is the native file format for Scratch 3.0. Crucially, an SB3 file is a ZIP file in disguise. It contains a specific internal structure required by MIT's Scratch engine. Inside an SB3 File Before understanding the converter, you have to understand
project.json['targets'][0]['name'] = 'MyModifiedSprite'