Echoing the sentiments of everyone else, I feel like the plateau you feel could possibly be reframed as the Japanese language learning journey itself (i.e. the Japanese language journey of a Japanese native). I feel like when we can get into the world of actual immersion and start consuming native content, we’ve “made” it.
However this really means that we’ve “made” it into the world of the native Japanese person who’s been immersing ever since they were born and away from the Japanese learner that can’t comprehend native content. I find that this jump is huge and as simias says, the wins are far a few in between, as we have to catch up to decades on decades of immersion.
Consider how much native language immersion we get in our daily lives, its basically 24/7 (so much so that we don’t even consider it immersion), similar to a Japanese person living in Japan, its Japanese 24/7. I feel that in order to bridge that gap we have to work quite hard to match the level of immersion they get, which really just means immersing a lot, a lot.
When we take a look at our own encyclopedic knowledge of the world, we know a ton of stuff from economics, to politics, to the sciences, to poetry, etc. But how did we get there? We had a ton of time (decades) to take in all that content, learn, and absorb it in our native language. So I feel that it isn’t a plateau/wall but more that we’re just a decade or so behind in immersion.
Therefore, I might recommend just significantly increasing your immersion. We simply need to catch up to the average Japanese native’s amount of immersion. Thankfully we are also more motivated to read Japanese books compared to the average (Japanese) person. This spreadsheet has a ton of good recommendations for all forms of media.
I also highly recommend Bunpro for grammar (N2, N1), as they have a ton of sentence examples per grammar point with SRS, and take up much less time for memorization compared to a book since the SRS does that for you. It also helps sharpen your reading since you need to read the example sentences for every item.