The idea of desk depth, PPI, is obsolete 1990s computer thinking.
None of that makes any sense because the original premise of computer work is a failure ergonomically.
Humans are not anatomically suited to sit at a desk for so-long. Their eyes are also not designed to stare at close objects shorter than 1 meter away.
Standing desk is a must, ontop of viewing distance 1.5 meters+. It wasn't possible in the 1990s, but now we know better.
77 inch is the absolute minimum size, BECAUSE, 1-1.5 meter viewing distance is the minimum for minimized eye strain, both focal and vergeance.