Deprecation errors when saving user profile data

[brylie]

When enabling the cc-authors plugin on WordPress 5.8 and editing a user profile, there are several deprecation errors displayed:

Deprecated: delete_usermeta is deprecated since version 3.0.0! Use delete_user_meta() instead. in /var/www/html/wp-includes/functions.php on line 5211 Warning: Cannot modify header information - headers already sent by (output started at /var/www/html/wp-includes/functions.php:5211) in /var/www/html/wp-includes/pluggable.php on line 1340 Warning: Cannot modify header information - headers already sent by (output started at /var/www/html/wp-includes/functions.php:5211) in /var/www/html/wp-includes/pluggable.php on line 1343