How do I ensure that the user can follow of multiple contents like topic, user

Question

I have a models like:

from app import db
from marshmallow_sqlalchemy import SQLAlchemyAutoSchema, fields
from datetime import datetime

class User(db.Model):
   __tablename__ = 'user'

   id = db.Column(db.Integer, db.ForeignKey('follower.followable_id'), primary_key=True)
   username = db.Column(db.String(32), nullable=False)
   email = db.Column(db.String(320), nullable=False)
   password_hash = db.Column(db.String(128), nullable=False)
   password_salt = db.Column(db.String(22), nullable=False)
   created_at = db.Column(db.DateTime, default=datetime.utcnow())

   user_comment = db.relationship('UserComment', back_populates='author')

   def to_json(self):
       return {'username': self.username, 'email': self.email}

   def get_id(self):
       return self.id


class Topic(db.Model):
   __tablename__ = 'topic'

   id = db.Column(db.Integer, db.ForeignKey('follower.followable_id'), primary_key=True)
   topic_name = db.Column(db.String(100))
   
class Follower(db.Model):
   __tablename__ = 'follower'

   id = db.Column(db.Integer, primary_key = True)
   follower_id = db.Column(db.Integer, db.ForeignKey('user.id'))
   followable_id = db.Column(db.Integer, db.ForeignKey('followable.followable_id'))

My goal is for the user to be able to follow topics and users. I tried to connect the id column of the user and topic table to the followable_id column of the follower table for this. And I linked the follower_id of the follower table to the user id.

In this case, I received an error when creating a topic table. (sqlalchemy.greetings.OperationalError: (pymysql.mistake.OperationalError) (1822, "Foreign key restriction could not be added. The missing index for the 'topic_ibfk_1' constraint in the referenced table is 'follower'")

https://stackoverflow.com/a/11618048/13975329 I took a reference from here and tried to create these tables but I couldn't.

How can I create a better design for user-topic follow mechanism and why does it give this error in topic table creation?