Neko a self-hosted virtual browser that runs in Docker and uses WebRTC technology.
https://neko.m1k1o.net/

Here is my Container Manager exported settings.

{
   "CapAdd" : [ "SYS_ADMIN" ],
   "CapDrop" : [],
   "cmd" : "/usr/bin/supervisord -c /etc/neko/supervisord.conf",
   "cpu_priority" : 50,
   "enable_publish_all_ports" : false,
   "enable_restart_policy" : false,
   "enable_service_portal" : null,
   "enabled" : true,
   "env_variables" : [
      {
         "key" : "PATH",
         "value" : "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
      },
      {
         "key" : "DEBIAN_FRONTEND",
         "value" : "noninteractive"
      },
      {
         "key" : "USER",
         "value" : "neko"
      },
      {
         "key" : "DISPLAY",
         "value" : ":99.0"
      },
      {
         "key" : "PULSE_SERVER",
         "value" : "unix:/tmp/pulseaudio.socket"
      },
      {
         "key" : "XDG_RUNTIME_DIR",
         "value" : "/tmp/runtime-neko"
      },
      {
         "key" : "NEKO_PASSWORD",
         "value" : "neko"
      },
      {
         "key" : "NEKO_PASSWORD_ADMIN",
         "value" : "admin"
      },
      {
         "key" : "NEKO_BIND",
         "value" : ":8080"
      },
      {
         "key" : "NEKO_USERNAME",
         "value" : "neko"
      },
      {
         "key" : "NEKO_EPR",
         "value" : "59000-59005"
      },
      {
         "key" : "NEKO_NAT1TO1",
         "value" : "192.168.11.5"
      },
      {
         "key" : "NEKO_FILE_TRANSFER_ENABLED",
         "value" : "true"
      }
   ],
   "exporting" : false,
   "id" : "a09751d176c47a3e471d4d520f85655fc08f73fe67c432c1690103763b6b3f96",
   "image" : "m1k1o/neko:chromium",
   "is_ddsm" : false,
   "is_package" : false,
   "labels" : {},
   "links" : [],
   "memory_limit" : 2147483648,
   "name" : "neko-chromium",
   "network" : [
      {
         "driver" : "bridge",
         "name" : "bridge"
      }
   ],
   "network_mode" : "bridge",
   "port_bindings" : [
      {
         "container_port" : 59000,
         "host_port" : 59000,
         "type" : "udp"
      },
      {
         "container_port" : 59001,
         "host_port" : 59001,
         "type" : "udp"
      },
      {
         "container_port" : 59002,
         "host_port" : 59002,
         "type" : "udp"
      },
      {
         "container_port" : 59003,
         "host_port" : 59003,
         "type" : "udp"
      },
      {
         "container_port" : 59004,
         "host_port" : 59004,
         "type" : "udp"
      },
      {
         "container_port" : 59005,
         "host_port" : 59005,
         "type" : "udp"
      },
      {
         "container_port" : 8080,
         "host_port" : 8181,
         "type" : "tcp"
      }
   ],
   "privileged" : false,
   "service_portals" : [],
   "shortcut" : {
      "enable_shortcut" : false,
      "enable_status_page" : false,
      "enable_web_page" : false,
      "web_page_url" : ""
   },
   "use_host_network" : false,
   "version" : 2,
   "volume_bindings" : [
      {
         "host_volume_file" : "/docker/neko-chromium",
         "is_directory" : true,
         "mount_point" : "/home/neko/Downloads",
         "type" : "rw"
      },
      {
         "host_volume_file" : "/docker/neko-chromium/chromium-policys.json",
         "is_directory" : false,
         "mount_point" : "/etc/chromium/policies/managed/policies.json",
         "type" : "ro"
      }
   ]
}

According to this, Here is the policies for chromium.

chromium-policys.json

{
    "DownloadRestrictions": 0,
    "AllowFileSelectionDialogs": true,
    "URLAllowlist": [
        "file:///home/neko/Downloads"
    ]
}

And then change download folder permission to 777, in my case is /volume1/docker/neko-chromium

Here is setting capture.