NGINX Proxy Manager makes things even easier! All you have to do is make certain that you have websockets enabled for the proxy settings to go to your Mastodon instance and don't forward via SSL because NPM is your SSL termination point. On your Mastodon instance's NGINX configuration, change the port to listen on port 80, comment out all of the SSL related options, and in the @proxy section change the proxy_set_header X-Forwarded-Proto $scheme; to proxy_set_header X-Forwarded-Proto https; This is just telling Mastodon a small lie so it thinks the traffic is encrypted. This is necessary to prevent a redirection loop which will break things.

You need to actually piece together those few to come up with one cohesive working instance. I can share with you the docker-compose.yml file that worked for me, if that will help.

version: '3'
services:
  db:
    restart: always
    image: postgres:14-alpine
    shm_size: 256mb
    networks:
      - internal_network
    healthcheck:
      test: ['CMD', 'pg_isready', '-U', 'postgres']
    volumes:
      - ./postgres14:/var/lib/postgresql/data
    environment:
      - 'POSTGRES_HOST_AUTH_METHOD=trust'

  redis:
    restart: always
    image: redis:7-alpine
    networks:
      - internal_network
    healthcheck:
      test: ['CMD', 'redis-cli', 'ping']
    volumes:
      - ./redis:/data

  # es:
  #   restart: always
  #   image: docker.elastic.co/elasticsearch/elasticsearch:7.17.4
  #   environment:
  #     - "ES_JAVA_OPTS=-Xms512m -Xmx512m -Des.enforce.bootstrap.checks=true"
  #     - "xpack.license.self_generated.type=basic"
  #     - "xpack.security.enabled=false"
  #     - "xpack.watcher.enabled=false"
  #     - "xpack.graph.enabled=false"
  #     - "xpack.ml.enabled=false"
  #     - "bootstrap.memory_lock=true"
  #     - "cluster.name=es-mastodon"
  #     - "discovery.type=single-node"
  #     - "thread_pool.write.queue_size=1000"
  #   networks:
  #      - external_network
  #      - internal_network
  #   healthcheck:
  #      test: ["CMD-SHELL", "curl --silent --fail localhost:9200/_cluster/health || exit 1"]
  #   volumes:
  #      - ./elasticsearch:/usr/share/elasticsearch/data
  #   ulimits:
  #     memlock:
  #       soft: -1
  #       hard: -1
  #     nofile:
  #       soft: 65536
  #       hard: 65536
  #   ports:
  #     - '127.0.0.1:9200:9200'

  web:
    #build: .
    #image: ghcr.io/mastodon/mastodon
    image: tootsuite/mastodon:latest
    restart: always
    env_file: .env.production
    command: bash -c "rm -f /mastodon/tmp/pids/server.pid; bundle exec rails s -p 3000"
    networks:
      - external_network
      - internal_network
    healthcheck:
      # prettier-ignore
      test: ['CMD-SHELL', 'wget -q --spider --proxy=off localhost:3000/health || exit 1']
    ports:
      - '127.0.0.1:3000:3000'
    depends_on:
      - db
      - redis
      # - es
    volumes:
      - ./public/system:/mastodon/public/system

  streaming:
    #build: .
    #image: ghcr.io/mastodon/mastodon
    image: tootsuite/mastodon:latest
    restart: always
    env_file: .env.production
    command: node ./streaming
    networks:
      - external_network
      - internal_network
    healthcheck:
      # prettier-ignore
      test: ['CMD-SHELL', 'wget -q --spider --proxy=off localhost:4000/api/v1/streaming/health || exit 1']
    ports:
      - '127.0.0.1:4000:4000'
    depends_on:
      - db
      - redis

  sidekiq:
    #build: .
    #image: ghcr.io/mastodon/mastodon
    image: tootsuite/mastodon:latest
    restart: always
    env_file: .env.production
    command: bundle exec sidekiq
    depends_on:
      - db
      - redis
    networks:
      - external_network
      - internal_network
    volumes:
      - ./public/system:/mastodon/public/system
    healthcheck:
      test: ['CMD-SHELL', "ps aux | grep '[s]idekiq\ 6' || false"]

  ## Uncomment to enable federation with tor instances along with adding the following ENV variables
  ## http_proxy=http://privoxy:8118
  ## ALLOW_ACCESS_TO_HIDDEN_SERVICE=true
  # tor:
  #   image: sirboops/tor
  #   networks:
  #      - external_network
  #      - internal_network
  #
  # privoxy:
  #   image: sirboops/privoxy
  #   volumes:
  #     - ./priv-config:/opt/config
  #   networks:
  #     - external_network
  #     - internal_network

networks:
  external_network:
  internal_network:
    internal: true

Maybe tell me where you're stuck and I can help?

Probably.

Though it was the official Mastodon container, and not a third party.