How to access state attribute

I try to access the state attributes of a sensor.
{{states.sensor.smartmeter_energy_power_curr}} returns
<template TemplateState(<state sensor.smartmeter_energy_power_curr=210.0; unit_of_measurement=W, friendly_name=SmartMeter ENERGY Power_curr, device_class=power @ 2022-12-24T09:22:55.423783+01:00>)>
but
{{state_attr('sensor.smartmeter_energy_power_curr','state')}} does not give the value and how do I get the timestamp?

Is there an easy way grasping the states? It’s a huge riddle to me for each sensor.

{{ states(’‘sensor.smartmeter_energy_power_curr’) }}

Templating - Home Assistant (home-assistant.io)

{{states('sensor.smartmeter_energy_power_curr')}} returns the current value only (e.g. 210.2)
so:
{{states.sensor.xy}} != {{states('sensor.xy')}}
?

Indeed…that is the value state…current value of field state
If you want data from the attributes then you need to use state_attr and specify the attribute name

ok, but how to access the timestamp visible in post 1? It sits behind an @ and any state selector fails.

That is not behind a @ sign, this is the value 'last updated

{{ states.sensor.archer_c1200_b_received.last_updated }}
of example: