bp_core_get_userid_from_nickname( string $nickname )

function bp_core_get_userid_from_nickname( $nickname ) {
	if ( empty( $nickname ) ) {
		return false;
	}

	$users = get_users( [
		'meta_key'    => 'nickname',
		'meta_value'  => $nickname,
		'number'      => 1,
		'count_total' => false
	] );

	$user = $users ? $users[0] : null;

	return apply_filters( 'bp_core_get_userid_from_nickname', ! empty( $user->ID ) ? $user->ID : null, $nickname );
}