vielen Dank für Eure Hilfestellungen. Das Problem ist gelöst, ich habe in den MQTT-Einstellungen das "full topic" falsch gesetzt.

Richtig ist: (Ich hatte prefix und topic vertauscht...)

Liebe Grüße

Martin

11:40:42 MQT: Attempting connection...
11:40:42 MQT: Connected
11:40:42 MQT: tele/Messgerät/LWT = Online (retained)
11:40:42 MQT: cmnd/Messgerät/POWER = 
11:40:42 MQT: tele/Messgerät/INFO1 = {"Module":"BlitzWolf SHP","Version":"8.1.0(lite)","FallbackTopic":"cmnd/Messgerät_fb/","GroupTopic":"cmnd/sonoffs/"}
11:40:42 MQT: tele/Messgerät/INFO2 = {"WebServerMode":"Admin","Hostname":"Kühlschrank","IPAddress":"192.168.1.122"}
11:40:42 MQT: tele/Messgerät/INFO3 = {"RestartReason":"Software/System restart"}
11:40:42 MQT: stat/Messgerät/RESULT = {"POWER":"ON"}
11:40:42 MQT: stat/Messgerät/POWER = ON (retained)
11:40:46 MQT: tele/Messgerät/STATE = {"Time":"2021-12-30T11:40:46","Uptime":"0T00:00:12","UptimeSec":12,"Vcc":3.466,"Heap":31,"SleepMode":"Dynamic","Sleep":50,"LoadAvg":21,"MqttCount":1,"POWER":"ON","Wifi":{"AP":2,"SSId":"frankyboy","BSSId":"98:9B:CB:D2:0E:10","Channel":6,"RSSI":90,"Signal":-55,"LinkCount":1,"Downtime":"0T00:00:06"}}
11:40:46 MQT: tele/Messgerät/SENSOR = {"Time":"2021-12-30T11:40:46","ENERGY":{"TotalStartTime":"2021-12-09T21:19:19","Total":3.789,"Yesterday":0.275,"Today":0.129,"Period":0,"Power":48,"ApparentPower":90,"ReactivePower":76,"Factor":0.53,"Voltage":218,"Current":0.413}}

Hier auch noch was zum lesen:
https://tasmota.github.io/docs/MQTT/

{"NAME":"NOUS A1","GPIO":[320,0,576,0,2656,2720,0,0,2624,32,0,224,0,0],"FLAG":0,"BASE":45}

In der Konsole wird folgendes angezeigt:

11:02:59.038 MQT: Verbindungsversuch...
11:02:59.073 MQT: verbunden
11:02:59.076 MQT: /SH/beweglich/Zwischen/nousA1_01/tele/LWT = Online (beibehalten)
11:02:59.078 MQT: /SH/beweglich/Zwischen/nousA1_01/cmnd/POWER = 
11:02:59.086 MQT: /SH/beweglich/Zwischen/nousA1_01/tele/INFO1 = {"Info1":{"Module":"NOUS A1","Version":"10.1.0(tasmota)","FallbackTopic":"cmnd/nousA101_fb/","GroupTopic":"/SH/beweglich/Zwischen/tasmotas/cmnd/"}}
11:02:59.101 MQT: /SH/beweglich/Zwischen/nousA1_01/tele/INFO2 = {"Info2":{"WebServerMode":"Admin","Hostname":"nousA1-01-0023","IPAddress":"192.168.188.74"}}
11:02:59.113 MQT: /SH/beweglich/Zwischen/nousA1_01/tele/INFO3 = {"Info3":{"RestartReason":"Software/System restart"}}
11:02:59.125 MQT: /SH/beweglich/Zwischen/nousA1_01/stat/RESULT = {"POWER":"ON"}
11:02:59.131 MQT: /SH/beweglich/Zwischen/nousA1_01/stat/POWER = ON
11:03:02.474 QPC: Reset
11:03:03.386 MQT: /SH/beweglich/Zwischen/nousA1_01/tele/STATE = {"Time":"2021-12-30T11:03:03","Uptime":"0T00:00:09","UptimeSec":9,"Heap":29,"SleepMode":"Dynamic","Sleep":50,"LoadAvg":19,"MqttCount":1,"POWER":"ON","Wifi":{"AP":1,"SSId":"Stecker","BSSId":"08:96:D7:F0:70:F8","Channel":11,"Mode":"11n","RSSI":64,"Signal":-68,"LinkCount":1,"Downtime":"0T00:00:03"}}
11:03:03.418 MQT: /SH/beweglich/Zwischen/nousA1_01/tele/SENSOR = {"Time":"2021-12-30T11:03:03","ENERGY":{"TotalStartTime":"2021-10-11T13:22:57","Total":1.045,"Yesterday":0.007,"Today":0.013,"Period": 1,"Power":363,"ApparentPower":370,"ReactivePower":73,"Factor":0.98,"Voltage":295,"Current":1.255}}

Die NousA1 liefert mir mit diesem Template die Verbrauchswerte:
{"NAME":"NOUS A1","GPIO":[320,0,576,0,2656,2720,0,0,2624,32,0,224,0,0],"FLAG":0,"BASE":45}