Restore the legacy row background opacity field for Beaver Builder.

row-bg-opacity.php

<?php

add_filter( 'fl_builder_register_settings_form', 'add_back_bb_row_bg_opacity', 10, 2 );
add_filter( 'fl_builder_node_settings', 'apply_opacity_to_bb_row_bg_color', 10, 2 );

function add_back_bb_row_bg_opacity( $form, $slug ) {
    if ( 'row' === $slug ) {
        $form['tabs']['style']['sections']['bg_color']['fields']['bg_opacity'] = array(
            	'type'    => 'unit',
		'label'   => __( 'Opacity', 'fl-builder' ),
		'default' => '100',
		'units'   => array( '%' ),
        );
    }
    return $form;
}

function apply_opacity_to_bb_row_bg_color( $settings, $node ) {
    if ( 'row' === $node->type ) {
        if ( isset( $settings->connections ) ) {
            $connections = (array) $settings->connections;
            if ( isset( $connections[ 'bg_color' ] ) && is_object( $connections[ 'bg_color' ] ) ) {
                $rgb = implode( ',', FLBuilderColor::hex_to_rgb( $settings->bg_color ) );
                $alpha = $settings->bg_opacity / 100;
                $settings->bg_color = "rgba($rgb, $alpha)";
            }
        }
    }
    return $settings;
}