2.80.2 crashes on “Backup” command

I just upgraded to 2.80.2 and requested a Backup. This error occurs. (I’ve removed the start of the paths for security reasons.)

When seeking help with this issue, you may be asked for some of the following information:
WordPress version 5.3.2
Current theme: Muz4Now – Merlin Child Theme (version 1.0.0)
Current plugin: WP-DBManager (version 2.80.2)
PHP version 7.1.33

Error Details
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An error of type E_ERROR was caused in line 428 of the file …/public_html/wp-content/plugins/wp-dbmanager/wp-dbmanager.php. Error message: Uncaught Error: Call to undefined function array_key_first() in …/public_html/wp-content/plugins/wp-dbmanager/wp-dbmanager.php:428
Stack trace:
#0 …/public_html/wp-content/plugins/wp-dbmanager/wp-dbmanager.php(255): check_backup_files()
#1 …/public_html/wp-content/plugins/wp-dbmanager/database-backup.php(52): execute_backup(‘/usr/local/bin/…’)
#2 …/public_html/wp-admin/admin.php(286): include(‘…/…’)
#3 {main}
thrown