Hi there,
Congrats on your first post in the Community! I'll be happy to share more info on journal entries in QBO.
At this time, QBO doesn't offer the feature which allows to insert a subtotal line into a journal entry. I know how important this feature is to you and I encourage you to send feedback about this to our engineers. You can do this by clicking the Gear icon and looking for Feedback. New product ideas and improvements are largely based on the feedback we get from users like you. Here's a helpful resource with more info on journal entries:
Let me know if you have questions.