What’s the meaningful difference between a monitor that is 32 inch vs. 27?

If both monitors have the same resolution (say 2560×1440 or 3840×2160), the 27″ will have higher pixels per inch (PPI) i.e., sharper image, cleaner text, finer details. For example: 27″ at 1440p ~108 PPI vs 32″ at the same resolution ~93 PPI.
If you go 32″ but keep a lower resolution (or don’t scale text properly) things may look a bit less sharp or slightly “bigger pixels”.