Can't upgrade WP 5.6 to 5.6.1: version-current.php is missing

As it says: I’m currently running WP 5.6 (on top of PHP 7.4.13 and CentOS 7.9.2009), and I got a notification that WP 5.6.1 is available, and that I should upgrade. I’m trying this via the "Upgrade Now" button on upgrade-core.php, and get:

Downloading update from https://downloads.wordpress.org/release/wordpress-5.6.1-no-content.zip… 
The authenticity of wordpress-5.6.1-no-content.zip could not be verified as no signature was found. 
Unpacking the update… 
Verifying the unpacked files… 
There has been a critical error on this website. Please check your site admin email inbox for instructions.

Checking the debug.log, I find:

[04-Feb-2021 21:48:11 UTC] PHP Warning: require(/var/www/html/example/wp-content/upgrade/version-current.php):
failed to open stream: No such file or directory in
/var/www/html/example/wp-admin/includes/update-core.php on line 949
[04-Feb-2021 21:48:11 UTC] PHP Fatal error:  require(): Failed opening required
'/var/www/html/example/wp-content/upgrade/version-current.php'
(include_path='.:/usr/share/pear:/usr/share/php:/var/www/html/example/wp-content/plugins/ssh-sftp-updater-support/phpseclib/')
in /var/www/html/example/wp-admin/includes/update-core.php on line 949

The error is correct: there is no file at wp-content/upgrade/version-current.php — in fact, there is no "upgrade" subdirectory under wp-content. I’m kinda lost; does anybody have any clues about what’s going on, and what I might to? Thanks!