I also ran into this issue. I spent a lot of time configuring UFW, DNS, and other things, but nothing worked. In the end, lowering the MTU to 1400 solved the problem. Honestly, I don’t even understand why this worked...

Just try to set DOCKER_OPTS="--mtu 1400" in /etc/default/docker.

Or update docker-compose.yml like this:

version: '3.8'

services:
  php:
    image: php:8.3-fpm
    container_name: php_app
    volumes:
      - .:/var/www/html
    ports:
      - "9000:9000"
    networks:
      - my_network

networks:
  my_network:
    driver: bridge
    driver_opts:
      com.docker.network.driver.mtu: 1400