Welcome @rbw - you’re super close!
If you define the callback output as a list
@app.callback([Output('kategorie-sls', 'figure')], ...)
then the return value must also be a length-1 list like
return [go.Figure(data=graph)]
or
return [{'data': graph}]
But if you don’t wrap in a list
@app.callback(Output('kategorie-sls', 'figure'), ...)
you should also not wrap the return in a list
return go.Figure(data=graph)
or
return {'data': graph}