The error indicates that a WordPress plugin or theme is requesting the “wp_filesize” function but the WordPress core is either corrupted or outdated and does not have that function yet.
Uncaught Error: Call to undefined function “wp_filesize” in /wp-admin/includes/image.php:249
WordPress 6.0 introduced the wp_filesize() function which should be used in favor of PHP’s filesize().
If you are still using an older WP version then just upgrade!
If you are running WordPress 6.0+ and still experience this error, then reinstall WordPress core files.
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