Jan Koch

Upon activation, this plugin uses the “automatic_updater_disabled” filter to prevent automatic updates from being installed. 
It does not offer configuration, not even an options page in WP Admin.
Simply install and activate the plugin to disable all automatic updates. Deactivate the plugin to re-enable all automatic updates.

Stop Automatic Updates

This plugin disables all automatic updates. No configuration needed.

Alex Moss

Peadig

Disables the default notification email sent by WordPress for an automatic core update. Simply activate the plugin to disable the notification email 🙂
<ul>
<li><a href="http://peadig.com/wordpress-plugins/disable-wordpress-core-update-email/" rel="nofollow ugc">Disable WordPress Core Update Email</a> Plugin homepage.</li>
<li>More <a href="http://peadig.com/wordpress-plugins/" rel="nofollow ugc">WordPress Plugins</a>.</li>
<li>Peadig: A <a href="http://peadig.com/" rel="nofollow ugc">WordPress Bootstrap</a> theme framework.</li>
</ul>

Disable WordPress Core Update Email

The simplicity of the plugin helps it be lightweight & easy to use.

That also means the one line of active PHP code that it consists of (it then being what WordPress recommends in its current documentation per https://wordpress.org/support/article/configuring-automatic-background-updates/#disable-emails-via-filter) is likely to continue to work exactly as expected unless WordPress were to completely overhaul its setup regarding this (with there appearing to be no plans for this.) Especially considering it's using a filter so it's even more flexible if things were to change in the future (won't outright break things due to a code error beyond WordPress doing a fundamental change to a core function like add_filter or __return_false & that'd then break the majority of plugins & themes out there [they'd need a good reason for doing so & it appears they obviously have no plans for doing that either.])

Does exactly what it says it does (even 5 years since last update)

Disables the default notification email sent by WordPress for an automatic core update. Simply activate the plugin to disable the notification email : …

Stop Automatic Updates vs Disable WordPress Core Update Email