I developed my own version of 3d sudoku because everything I could find online seemed gimmicky, whereas this is (in my opinion) a true generalisation of sudoku to three dimensions. While regular sudoku has vertical columns and horizontal rows, my 3d sudoku adds what I decided to call towers for lack of a better description, which are essentially the same as rows and columns, just in the perpendicular direction.

Each number 1-8 must be used exactly once in each row, column and "tower" (I visualise the different layers on top of each other, and so it would appear to stick out from the ground like a tower when rested on a flat surface) and 2x2x2 box. In the image attached I drew each layer of the 8x8x8 cube next to eachother and connected them by arrows that mean that one is on top of or below the next. The two 8x8 square layers next to eachother share a 2x2x2 box.

Despite my best efforts, what I drew is not, strictly, an extension of sudoku into 3 dimensions, but rather an extension of 4x4 sudoku into 3 dimensions. To extend regular 9x9 sudoku into 3 dimensions I would need to draw a 27x27x27 cube containing nearly 20,000 cells as opposed to the 512 of my 8x8x8 sudoku or the mere 81 of regular sudoku.

I thought of it just a few hours ago and spent the time since them drawing it, writing this and writing something similar on a reddit post, so I don't know whether the regular strategies will continue to apply. Singles definitely will, and I think doubles, triples and quads will still apply, but I can't easily visualise pointing pairs and box-line reduction in three dimensions, nor X-Wings and other more complicated tactics. I suspect that most methods of working out sudokus will either work in my 3d sudoku or have a close analogue in my 3d sudoku, but that is just conjecture.

I couldn't attach the image because of the file size, so here's a website that I uploaded it to instead. https://imgur.com/a/HDMuCZ2