Identifying a high impact idea and rapidly prototyping, particularly with 0 company context, is often hard. But even then, getting from prototype to product is very hard. There are often very good reasons why things are the way they are, and these are hard to identify as a new and junior engineers. Generally, this is the kind of thing bigger companies want from newly hired staff+ engineers, not juniors. For better or for worse, people are going to treat something innovative from a junior engineer with far more skepticism. Not to mention, there can very often be politics involved. My experience is that the most palatable good ideas are those most grounded in data, like saving money on infrastructure spend.
My advice to junior engineers is basically the same as it always has been: work enthusiastically, volunteer for as much as you can, watch what senior people are doing and why, ask questions, be useful to your manager and your teammates, focus on smaller, team-local (but still useful!) innovations.
There’s a lot that AI makes possible to do, and to do rapidly, but it adds many traps around not understanding the big picture, missing requirements, being too narrowly focused, or not grounding claims, all of which make it challenging to know that you’re working on the right thing as a junior engineer. That’s not to say one shouldn’t, but I’d be very careful and not get sucked into spending too much time on these kinds of things.