I was told by an automotive tyre guy that pressure loss with nitrogen is slightly less.
The molecule is larger than the oxygen molecule.
Rubber does a pretty good job at containing air/gas. At a molecular level, some gas very slowly leaks through the material. It might take several weeks for a pressure loss to become evident - maybe months - but it will gradually deflate.
The higher the inflation pressure, the greater/faster the loss.
Makes sense. However, at the end of the discussion, I opted for regular air. I don't mind recharging the tyres every few months when/if required.