import gradio as gr

with gr.Blocks() as demo:
    show_box = gr.Checkbox()

    @gr.render(inputs=show_box)
    def render(show_box):
        if show_box:
            textbox = gr.Textbox()
            textbox2 = gr.Textbox()
            textbox.submit(lambda x:x, textbox, textbox2)
        else:
            gr.Markdown("Hidden textbox")

demo.launch(debug=True)