I found a section on the Slack API page that explains what's going on with your interactive component!

Everything I am about to go over is in the Responding to the interaction section of the official documentation.

There are two steps to responding to an interaction:

1. Acknowledgment response - send an OK 200 back to slack within 3 seconds of receiving the request payload. The text you send with this response will not alter the contents of the current slack message.
2. Composed response - send your updated message to slack using a POST request and the response_url they package in the request payload.

So the reason OP's code does not work is that Slack does no longer accept a full message as direct response to an interaction. Instead all response messages need to be send to the response_url.

However, to enable backwards compatibility it is still possible to respond directly with message including attachments, but not with messages containing layout blocks.

Code

Here is the code I used to substitute the original button message with the text "Hi Erik!"

import requestsfrom flask import Flask, json, requestapp = Flask(__name__) #create the Flask app@app.route('/slash', methods=['POST'])def slash_response():                    """ endpoint for receiving all slash command requests from Slack """    # blocks defintion from message builder    # converting from JSON to array    blocks = json.loads("""[        {            "type": "section",            "text": {                "type": "plain_text",                "text": "Please select an option:",                "emoji": true            }        },        {            "type": "actions",            "elements": [                {                    "type": "button",                    "text": {                        "type": "plain_text",                        "text": "Click me",                        "emoji": true                    },                    "value": "button_1"                }            ]        }    ]""")    # compose response message        response = {        "blocks": blocks    }    ## convert response message into JSON and send back to Slack    return json.jsonify(response)@app.route('/interactive', methods=['POST'])def interactive_response():                    """ endpoint for receiving all interactivity requests from Slack """    # compose response message       data = json.loads(request.form["payload"])    response = {        'text': 'Hi Erik!',         }    requests.post(data['response_url'], json=response)    return '' if __name__ == '__main__':    app.run(debug=True, port=8000) #run app in debug mode on port 8000