Magento 2: Command returned non-zero exit code during submission on marketplace

I would suggest the below steps to fix this kind of issue.

1) Remove var/* generation/* and try to run that command again. And provide proper permission for var/ generation and pub folder.

2) Check logs and see if you find any issue, please fix it and try again.

3) Try to update the PHP.INI values.

php.ini values are: post_max_size = 1024M upload_max_filesize = 1024M memory_limit = 3G max_execution_time = 500 

Hope this will help you.

Change the mode and skip the compilation:

php magento deploy:mode:set production --skip-compilation php magento setup:static-content:deploy en_GB 

Magento default locale is en_US so you have to define your language.

If that fails, make sure your /var and pub/ have the correct permissions

It could be that your PHP is exhausted so increasing the limit in php.ini should help but skipping the compilation and compiling after switch is a good workaround.

Also, make sure your store in use has a valid theme selected, it might be that you are using a theme that doesn't exist in the system.

This error means that the extension prevents product and category pages from being cached by Varnish. One possible cause is using cacheable="false" in one or more blocks on product and category pages.

Additional resources: https://devdocs.magento.com/guides/v2.4/config-guide/varnish/config-varnish.html