Where to put bussiness logic in Django (DRF)?

Despite it is very popular question and already has a lot of answers, I don't really get it. I understand that putting tons of logic in views is not a good idea, so in my projects I create files like utils, logic, helpers. But the problem is that I don't know where should I call those "logical" functions? Should I make them as a property or method of model instance, or should I call it in a view passing model instance as an argument? For example in my current pet-project I have Question and Answer models. Question has is_solved Boolean (default=False) field which means if the question is solved or not, and Answer has is_solving Boolean field (default=False) as well and if True, it means that the answer helped to solve an issue. I have a function in logic file which handles it. Here is the code:

def vote_answer_solving(answer: Answer, related_question: Question):

    if answer.is_solving:
        answer.is_solving = False
        related_question.is_solved = False
    else:
        if related_question.question_answers.filter(is_solving=True).exists():
            is_solving_answer = related_question.question_answers.get(is_solving=True)
            is_solving_answer.is_solving = False
            is_solving_answer.save()
        answer.is_solving = True
        related_question.is_solved = True

    related_question.save()
    answer.save()

I call it in a view, where user requests the endpoint and the logic is handled by the function. I don't really know, maybe I should place the logic in models save method, so when it gets an answer with is_solving=True, related question status is_solved=False changes to True.

This was just the example of my general misunderstanding of how to make my code cleaner, especially when I should place logic in similar situation to views (call the separeted function in there) or handle it on the level of model managers or save method.

I do really hope if someone helps me someway by answering the question or recommending some books, articles related to the issue to read where I can find the appropriate solution. Thanks in advance!