I think we've always had this mental model which needs to change that senior engineers and product managers scope and design features, IC developers (including juniors for simpler work) implement them, and then senior engineers participate in code review.
Right now I can't see the value in having a junior engineer on the team who is unable to think about how certain features should be designed. The junior engineer who previously spent his time spinning tires trying to understand the codebase and all the new technologies he has to get to grips with should instead spend that time trying to figure out how that feature fits into the big picture, consider edge cases, and then propose a design for the feature.
There are many junior engineers who I wouldn't trust with that kind of work, and honestly I don't think they are employable right now.
In the short term, I think you just need to communicate this additional duty of care to make sure that your pull requests are complete because otherwise there's an asymmetry of workload and judge those interns and juniors on how respectful of that they are.