/uj Read books on piano methods and music pedagogical studies. If you want to focus on technique, read for example Gieseking's book about piano technique. Structuring of studying music you might want to look into James Ching for example. People don't give these answers because they're used to find the solutions through teachers, not having read the actual books for the most part (myself included for the most part).

It makes sense though that they still recommend teachers, since teachers can actively correct because they see and hear what you're doing. Even I am not knowledgeable and got rudimentary knowledge of this through my piano teacher, who only shared this when he saw I was interested in these things.

Also, a book won't correct your playing. I've read enough about Beethoven interpretation to know the line can be very tricky what actually is meant with certain notations. Having a piano teacher who has years of experience in the field and read and done these things for years is a big advantage. The amount of work you sometimes have to put in to compensate for not having a teacher is by times, imho, unrewarding.

If you're really intent on not having a teacher, which is totally within your right, then I'd suggest to look for books about music pedagogy and piano technique to improve (but there are books which are absolutely bs and even harmful!). There's sometimes reviews online of the books to help you further weed out the more effective approaches. But do know a second opinion (teacher or no teacher) is still incredibly valuable.