does the website work on the host where Composer was executed?
If it works on that host but not on the public hosting, then you should try transferring the files again and make sure no old files stay left over.
If it doesn't work locally either, you should try re-installing all Composer dependencies by deleting vendor and running composer install again.
If there's an issue with composer install, you might need to delete the lock file to make sure you are fully upgrading.
