this is my container config for element/matrix podman containers do not run as root so you have to get the file privileges right on the volumes mapped into the containers. i used top to find out what user the services were running as. you can see there are some settings there where you can change the user if you are having permissions problems

{ pkgs, modulesPath, ... }:

{

  imports = [
    (modulesPath + "/virtualisation/proxmox-lxc.nix")
  ];

  security.pki.certificateFiles = [ "/etc/ssl/certs/ca-certificates.crt" ];

  system.stateVersion = "23.11";
  system.autoUpgrade.enable = true;
  system.autoUpgrade.allowReboot = false;

  nix.gc = {
    automatic = true;
    dates = "weekly";
    options = "--delete-older-than 14d";
  };

  services.openssh = {
    enable = true;
    settings.PasswordAuthentication = true;
  };

  users.users.XXXXXX = {
    isNormalUser = true;
    home = "/home/XXXXXX";
    extraGroups = [ "wheel" ];
    shell = pkgs.zsh;
  };

  programs.zsh.enable = true;

  environment.etc = {
    "fail2ban/filter.d/matrix-synapse.local".text = pkgs.lib.mkDefault (pkgs.lib.mkAfter ''
      [Definition]
      failregex = .*POST.* - <HOST> - 8008.*\n.*\n.*Got login request.*\n.*Failed password login.*
                  .*POST.* - <HOST> - 8008.*\n.*\n.*Got login request.*\n.*Attempted to login as.*\n.*Invalid username or password.*
    '');
  };

  services.fail2ban = {
    enable = true;
    maxretry = 3;
    bantime = "10m";
    bantime-increment = {
      enable = true;
      multipliers = "1 2 4 8 16 32 64";
      maxtime = "168h";
      overalljails = true;
    };
    jails = {
      matrix-synapse.settings = {
        filter = "matrix-synapse";
        action = "%(known/action)s";
        logpath = "/srv/logs/synapse.json.log";
        backend = "auto";
        findtime = 600;
        bantime  = 600;
        maxretry = 2;
      };
    };
  };

  virtualisation.oci-containers = {
    containers = {

      postgres = {
        autoStart = false;
        environment = {
          POSTGRES_USER = "XXXXXX";
          POSTGRES_PASSWORD = "XXXXXX";
          LANG = "en_US.utf8";
        };
        image = "docker.io/postgres:14";
        ports = [ "5432:5432" ];
        volumes = [
          "/srv/postgres:/var/lib/postgresql/data"
        ];
        extraOptions = [
          "--label" "io.containers.autoupdate=registry"
          "--pull=newer"
        ];
      };

      synapse = {
        autoStart = false;
        environment = {
          LANG = "C.UTF-8";
#          UID="0";
#          GID="0";
        };
 #       user = "1001:1000";
        image = "ghcr.io/element-hq/synapse:latest";
        ports = [ "8008:8008" ];
        volumes = [
          "/srv/synapse:/data"
        ];
        log-driver = "json-file";
        extraOptions = [
          "--label" "io.containers.autoupdate=registry"
          "--log-opt" "max-size=10m" "--log-opt" "max-file=1" "--log-opt" "path=/srv/logs/synapse.json.log"
          "--pull=newer"
        ];
        dependsOn = [ "postgres" ];
      };

      element = {
        autoStart = true;
        image = "docker.io/vectorim/element-web:latest";
        ports = [ "8009:80" ];
        volumes = [
          "/srv/element/config.json:/app/config.json"
        ];
        extraOptions = [
          "--label" "io.containers.autoupdate=registry"
          "--pull=newer"
        ];
#        dependsOn = [ "synapse" ];
      };

      call = {
        autoStart = true;
        image = "ghcr.io/element-hq/element-call:latest-ci";
        ports = [ "8080:8080" ];
        volumes = [
          "/srv/call/config.json:/app/config.json"
        ];
        extraOptions = [
          "--label" "io.containers.autoupdate=registry"
          "--pull=newer"
        ];
      };

      livekit = {
        autoStart = true;
        image = "docker.io/livekit/livekit-server:latest";
        ports = [ "7880:7880" "7881:7881" "50000-60000:50000-60000/udp" "5349:5349" "3478:3478/udp" ];
        cmd = [ "--config" "/etc/config.yaml" ];
        entrypoint = "/livekit-server";
        volumes = [
          "/srv/livekit:/etc"
        ];
        extraOptions = [
          "--label" "io.containers.autoupdate=registry"
          "--pull=newer"
        ];
      };

      livekitjwt = {
        autoStart = true;
        image = "ghcr.io/element-hq/lk-jwt-service:latest-ci";
        ports = [ "7980:8080" ];
        environment = {
          LK_JWT_PORT = "8080";
          LIVEKIT_URL = "wss://livekit.XXXXXX.dynu.net";
          LIVEKIT_KEY = "XXXXXX";
          LIVEKIT_SECRET = "XXXXXX";
        };
        entrypoint = "/lk-jwt-service";
        extraOptions = [
          "--label" "io.containers.autoupdate=registry"
          "--pull=newer"
        ];
      };

    };
  };

}