Hello,
Can you please share the error message when updating the package via Composer? Please try to use this command to update Meta Box packages and let me know if it works.
rm -rf vendor && composer clear-cache && composer install
Following the documentation https://docs.metabox.io/integration/#why-cant-i-update-with-composer
The 404 Not Found is normal. Composer doesn't use that URL directly to get the info about the packages.