This isn’t a data problem, it is a code issue.
In your view, you have:
category_posts = Post.objects.filter(category__iexact=cats.title().replace('-', ' '))
Then, your definition of the Post model contains:
category= models.ForeignKey(Category, max_length=60, on_delete=models.CASCADE, related_name="cats")
So, the problem is with your filter.
Post.object.filter(category...)
category is a reference to the Model, not a field within the model. You’re trying to perform a string comparison (iexact) against the model. However, I believe what you’re really trying to match here is the name field within the Category model, which means your filter should be:
Post.object.filter(category__name__iexact=...