A nonexistent object was used in an `State` of

Dash Python
4

I assume this to be the problem. What you are doing here is creating content dynamically. But instead of using pattern matching ID’s and callbacks, you have a fixed ID for the components.

Instead of creating the components on each call (on each change of selected_option) I would just toggle the visibility of the components via the style parameter.

Here an example:

Applied to your use case:

import dash
from dash import dcc, html, Input, Output


app = dash.Dash(__name__)

app.layout = html.Div(
    [
        html.Div(
            [
                dcc.Dropdown(
                    id='main_dropdown',
                    options=[1, 2],
                    multi=False,
                    value=1
                )
            ]
        ),
        html.Div(
            id='additional_content',
            children=[
                dcc.Dropdown(
                    id='additional_dropdown_1',
                    options=[3, 4],
                    multi=False,
                ),
                dcc.Dropdown(
                    id='additional_dropdown_2',
                    options=[5, 6],
                    multi=False,
                )
            ]
        ),
        html.Button(id='btn', children='dummy')
    ]
)


@app.callback(
    Output('additional_content', 'style'),
    Input('main_dropdown', 'value'),
)
def show_hide(selection):
    if selection == 1:
        return {}
    return {'display': 'none'}


if __name__ == '__main__':
    app.run(debug=True, port=8070)