to get sb3 i use extension called resources saver, it lets u download all asset from the itch.io game. click play button and inspect game and u find html in devtools and click that, now use extension to start downloading
if it doesn't work and ur html has less try again until html is valid. also works on zip htmls too, sometimes u get assets folder. if no sb3 or project.json grab the json file by finding it in devtools network
this doesn't work on cocrea mods bc it gives no content u have to manually download every asset from devtools, con is u don't get full pack and no project.json som thinfs r still missing
resources saver is useable in devtools, switch ur ui to legacy in the settings if not available after installed