The Planiverse by A. K. Dewdney is also a great read on this subject - its less of an allegory than Flatland and focuses more on what the physiology and society of 2D life might look like. Worth a look.
And of course Schlegel diagrams which are commonly used for visualizing four-dimensional polytopes.
It’s been over 100 years (very close in time to the publication of flatland) and I don’t think anyone has proposed an alternative diagram of a 4 cube/hypercube/Tesseract.