Modifying, Editing, and Saving Post Meta Values in the Gutenberg Block Editor: https://jeffreycarandang.com/how-to-enable-read-and-update-post-meta-in-the-wordpress-block-editor-gutenberg/(opens in a new tab)

saveMeta.js

import { __ } from '@wordpress/i18n';
import { useSelect, useDispatch } from '@wordpress/data';
import { PanelBody, PanelRow, TextControl } from '@wordpress/components';
import { InspectorControls } from '@wordpress/block-editor';

/**
 * My Custom Block
 */
const MyCustomBlock = () => {
    const META_KEY = 'custom_post_meta';
    const { editPost } = useDispatch('core/editor');
    const meta = useSelect((select) =>
        select('core/editor').getEditedPostAttribute('meta')
    );
    const { [META_KEY]: customMeta } = meta;

    const onCustomMetaChange = (newValue) => {
        editPost({
            meta: { ...meta, [META_KEY]: newValue },
        });
    };

    return (
        <div>
            <InspectorControls>
                <PanelBody title={__('Settings', 'textdomain')}>
                    <PanelRow>
                        <TextControl
                            label={__('Custom Meta', 'textdomain')}
                            value={customMeta}
                            onChange={onCustomMetaChange}
                        />
                    </PanelRow>
                </PanelBody>
            </InspectorControls>
        </div>
    );
};