I can't subscribe to MQTT topic referring to single field

I am a newbie in LORA and TTN and try to subscribe a single payload-field, which I have published by Arduino and Dragino shield. In the TTN console (Apllication data) I can see the “payload” and the decoded field “led:”.

When I try to subscribe this single field with an Android client app like MQTT dash or MQTT dashboard or an other app or other Windows app or program I can only see all data, but I can’t see the single field “payload” or “led”.

For all data I used AppID/devices/deviceID/up. That was ok.
For a single field I used AppID/devices/deviceID/up/led, but here I saw no result.Why?

In my opinion, so far i have undertood MQTT in TTN, the payloads in TTN were automatically published as topics and the client, which wants to subscribe a payload-field, must only attach the name of the encoded payload field to the path for all data.

I don’t understand it, please help.

You did right, however, https://status.thethings.network shows:

Uplink Fields on MQTT Disabled

Identified - For performance reasons we unfortunately had to disable publishing Uplink Fields to MQTT in our EU region. This means that the values from payload decodes are no longer published to individual [AppID]/devices/[DevID]/up/[Field] topics. Until this is resolved, you can subscribe to [AppID]/devices/[DevID]/up and read the payload_fields field from the uplinks you receive there.
Nov 18, 11:00 CET

See also MQTT used to work fine, but stopped getting data and TTN uplink node Node-Red connected but not working.

Thanks for the answer