Is your feature request related to a problem? Please describe.
When studying from the parent deck, Anki merges all review cards into one queue and all new cards into another. This means new cards are not shown alongside the review cards from their own subdeck, which leads to constant unnecessary switching between topics.
Describe the solution you’d like.
An option that preserves subdeck grouping inside the parent deck, so that new cards from a subdeck appear immediately before or after that subdeck’s review cards when studying the parent deck.
Describe alternatives you’ve considered.
Studying each subdeck individually or using filtered decks, but both require switching decks manually and have other drawbacks compared to reviewing from the parent deck.
I think you’ve already found that option – it’s the subdeck itself. The point of studying through the parent deck is to study all of your cards together. If you want to make sure cards stay close with their subdeck-makes, you should study each subdeck on its own.
Studying each subdeck individually does keep cards grouped, but it’s not ideal when you have many subdecks with only a few reviews per day in each subdeck. In that situation, any card I get wrong comes back far too quickly because the subdeck’s queue is tiny. That means the spacing is distorted, so just using the subdecks is less effective than studying from the parent deck.
An option to place each subdeck’s new cards next to its review cards would make learning smoother by keeping related material together and reducing unnecessary topic‑shifts, while still preserving the benefits of benefits of studying with the parent deck instead of the subdecks.
I know this doesn’t answer your question, but I’d like to point out that topic-shifts are a good thing.
Studying multiple topics in a non-linear fashon is known as interleaving and as far as I know scientifically proven to be more effective than block learning. At least anecdotally, I can tell you that it works perfectly fine. I always do that with my cards which have a verity of topics (from psychology to language learning cards, I study everything with interleaving in anki).