Gavin Bloodworth

@florismk Thanks for providing this information. It has helped me fix the same problem with my companies website. I also had the same define() present in my wp-config.php file which disables the builtin wordpress autoupdater.
I did some research and found the reason why the plugin auto-update is missing in some installations. And why that “define(‘AUTOMATIC_UPDATER_DISABLED’, true);” is put there.
The answer is it depends on how you actually installed the wordpress instance in the first place. If you installed it manually, following some documented steps from a page like https://ww.wp.xz.cn/support/article/how-to-install-wordpress/ you will not have this autoupdater disable defined.
However, many web hosting companies provide an Application Installer and Software Automation tools as features available in Hosting Manger (cPanel). In my case, I used Installatron to install wordpress on my web server. It was Installatron that placed that autoupdater disable line in wp-config.php. That is because Installatron has its own autoupdate features for wordpress, plugins and themes. Which can be configured as part of Installatron settings. If you want wordpress to take care of these autoupdates instead of Installatron, just delete the line in wp-config.php as advised by Floris. But if you do that, you should also disable all autoupdates in Installatron. Otherwise, there is a chance they both might try and perform an autoupdate at the same time and cause a problem.
This would also be the case if your web hosting provider has another Application Installer program and you used it (Softaculous, Fantastico, etc).

Gavin