A dynamic Gutenberg block with block.json and render.php

npx @wordpress/create-block@4.99.0 category-posts --variant dynamic --namespace lw --title "Category Posts"
cd category-posts
npm install --save-dev --save-exact @wordpress/scripts@37.0.0
npm run build

category-posts/                 (abridged)
├── category-posts.php          plugin header and block registration
├── package.json                build/start scripts with --blocks-manifest
├── readme.txt
├── src/
│   └── category-posts/
│       ├── block.json
│       ├── index.js
│       ├── edit.js
│       ├── render.php
│       ├── view.js             not loaded by this example
│       ├── style.scss
│       └── editor.scss
└── build/                      written by npm start / npm run build
    ├── blocks-manifest.php
    └── category-posts/
        ├── block.json
        ├── index.js
        ├── index.asset.php
        ├── index.css
        ├── style-index.css
        └── render.php

{
	"scripts": {
		"build": "wp-scripts build --webpack-copy-php --blocks-manifest",
		"start": "wp-scripts start --webpack-copy-php --blocks-manifest"
	}
}

{
	"$schema": "https://schemas.wp.org/trunk/block.json",
	"apiVersion": 3,
	"name": "lw/category-posts",
	"version": "0.1.0",
	"title": "Category Posts",
	"category": "widgets",
	"icon": "list-view",
	"description": "Lists the latest posts of one category, rendered on the server.",
	"attributes": {
		"categoryId": {
			"type": "integer",
			"default": 0
		},
		"count": {
			"type": "integer",
			"default": 5
		}
	},
	"usesContext": [ "postId" ],
	"supports": {
		"html": false,
		"align": [ "wide", "full" ],
		"color": {
			"background": true,
			"text": true,
			"link": true
		},
		"spacing": {
			"margin": true,
			"padding": true
		},
		"typography": {
			"fontSize": true
		}
	},
	"textdomain": "category-posts",
	"editorScript": "file:./index.js",
	"editorStyle": "file:./index.css",
	"style": "file:./style-index.css",
	"render": "file:./render.php"
}

<?php
/**
 * Plugin Name:       Category Posts
 * Description:       Server-rendered block that lists the latest posts of one category.
 * Version:           0.1.0
 * Requires at least: 6.9
 * Requires PHP:      7.4
 * Author:            Lukas Wojcik
 * License:           GPL-2.0-or-later
 * License URI:       https://www.gnu.org/licenses/gpl-2.0.html
 * Text Domain:       category-posts
 *
 * @package Lw
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit; // Exit if accessed directly.
}

/**
 * Registers every block listed in build/blocks-manifest.php.
 *
 * The manifest is generated by wp-scripts (--blocks-manifest), so WordPress
 * does not have to read and decode each block.json on every request.
 */
function lw_category_posts_block_init() {
	wp_register_block_types_from_metadata_collection(
		__DIR__ . '/build',
		__DIR__ . '/build/blocks-manifest.php'
	);
}
add_action( 'init', 'lw_category_posts_block_init' );

<?php
/**
 * Server-side rendering of the lw/category-posts block.
 *
 * Variables provided by WordPress:
 *
 * @var array    $attributes Block attributes, defaults from block.json applied.
 * @var string   $content    Inner content (always empty for this block).
 * @var WP_Block $block      Block instance: name, context, parsed block.
 *
 * @package Lw
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit; // Exit if accessed directly.
}

$lwcp_category_id = isset( $attributes['categoryId'] ) && is_int( $attributes['categoryId'] )
    ? $attributes['categoryId'] : 0;
$lwcp_count = isset( $attributes['count'] ) && is_int( $attributes['count'] )
    ? $attributes['count'] : 5;
if ( $lwcp_category_id < 1 ) {
    return;
}
if ( $lwcp_count < 1 || $lwcp_count > 10 ) {
    $lwcp_count = 5;
}
$lwcp_term        = $lwcp_category_id ? get_term( $lwcp_category_id, 'category' ) : null;

// Render nothing until a valid category has been chosen.
if ( ! $lwcp_term instanceof WP_Term ) {
	return;
}

// Do not list the post that contains the block (context from "usesContext").
$lwcp_current_id = isset( $block->context['postId'] ) ? absint( $block->context['postId'] ) : 0;

$lwcp_posts = get_posts(
	array(
		'category__in' => array( $lwcp_term->term_id ),
        'suppress_filters' => false,
		'numberposts'  => $lwcp_count,
		'post_status'  => 'publish',
		'has_password' => false,
		'exclude'      => $lwcp_current_id ? array( $lwcp_current_id ) : array(),
	)
);
?>
<div <?php // Core escapes the returned attribute values.
// phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- Core-generated wrapper attributes.
echo get_block_wrapper_attributes(); ?>>
	<?php if ( empty( $lwcp_posts ) ) : ?>
		<p><?php esc_html_e( 'No posts in this category yet.', 'category-posts' ); ?></p>
	<?php else : ?>
		<ul class="wp-block-lw-category-posts__list">
			<?php foreach ( $lwcp_posts as $lwcp_post ) : ?>
				<li>
					<a href="<?php echo esc_url( get_permalink( $lwcp_post ) ); ?>"><?php echo esc_html( get_the_title( $lwcp_post ) ); ?></a>
					<time datetime="<?php echo esc_attr( get_the_date( 'c', $lwcp_post ) ); ?>"><?php echo esc_html( get_the_date( '', $lwcp_post ) ); ?></time>
				</li>
			<?php endforeach; ?>
		</ul>
	<?php endif; ?>
</div>

import { registerBlockType } from '@wordpress/blocks';
import './style.scss';
import Edit from './edit';
import metadata from './block.json';

// No fallback HTML: only the block comment and attributes are stored.
registerBlockType( metadata.name, {
	edit: Edit,
    save: () => null,
} );

import { __ } from '@wordpress/i18n';
import { InspectorControls, useBlockProps } from '@wordpress/block-editor';
import {
	Notice,
	PanelBody,
	Placeholder,
	RangeControl,
	SelectControl,
	Spinner,
} from '@wordpress/components';
import { useSelect } from '@wordpress/data';
import { store as coreStore } from '@wordpress/core-data';
import { decodeEntities } from '@wordpress/html-entities';
import { ServerSideRender } from '@wordpress/server-side-render';
import metadata from './block.json';
import './editor.scss';

// Same query shape as the core Latest Posts block uses for its category list.
const CATEGORIES_QUERY = { per_page: -1, _fields: 'id,name', context: 'view' };

export default function Edit( { attributes, setAttributes } ) {
	const { categoryId, count } = attributes;
	const blockProps = useBlockProps();

    const { categories, categoryError } = useSelect( ( select ) => {
        const store = select( coreStore );
        const args = [ 'taxonomy', 'category', CATEGORIES_QUERY ];
        return {
            categories: store.getEntityRecords( ...args ),
            categoryError: store.getResolutionError( 'getEntityRecords', args ),
        };
    }, [] );

	const options = [
		{ value: '0', label: __( '— Select a category —', 'category-posts' ) },
		...( categories ?? [] ).map( ( term ) => ( {
			value: String( term.id ),
			label: decodeEntities( term.name ),
		} ) ),
	];

	return (
		<>
			<InspectorControls>
				<PanelBody title={ __( 'Settings', 'category-posts' ) }>
					{ categoryError ? (
                        <Notice status="error" isDismissible={ false }>
                            { __( 'Categories could not be loaded.', 'category-posts' ) }
                        </Notice>
                    ) : categories ? (
						<SelectControl
							__next40pxDefaultSize
							__nextHasNoMarginBottom
							label={ __( 'Category', 'category-posts' ) }
							value={ String( categoryId ) }
							options={ options }
							onChange={ ( value ) =>
								setAttributes( { categoryId: Number( value ) } )
							}
						/>
					) : (
						<Spinner />
					) }
					<RangeControl
						__next40pxDefaultSize
						__nextHasNoMarginBottom
						label={ __( 'Number of posts', 'category-posts' ) }
						value={ count }
						min={ 1 }
						max={ 10 }
						onChange={ ( value ) =>
							setAttributes( { count: value ?? 5 } )
						}
					/>
				</PanelBody>
			</InspectorControls>
			<div { ...blockProps }>
				{ categoryId ? (
					<ServerSideRender
						block={ metadata.name }
						attributes={ attributes }
						skipBlockSupportAttributes
					/>
				) : (
					<Placeholder
						icon="list-view"
						label={ __( 'Category Posts', 'category-posts' ) }
						instructions={ __(
							'A category selection in the block settings enables the preview.',
							'category-posts'
						) }
					/>
				) }
			</div>
		</>
	);
}