i used thios short python script to concatonate and save a new csv with the idnex beeing a datetime dtype:
df['ts']= pd.to_datetime(df['ts'])
df=df.set_index(df['ts'])
df=df.drop(columns=['ts'])
df.index = df.index.tz_convert('Europe/Berlin')
df.to_csv('C:\\Privat\\Python_VSC\\Spotify\\MyData_2025\\Data_concat.csv')
in the json's the ts column was given in UTC. (i concatonated the Json's into a csv.
Now i tried opening the new File in a jupyter notebook only to get that response:
df.index.dtype