I personally think to add a dark mode to Inventor is a great idea, as many users who use Inventor are staring into there monitors/screen for a long period of time and I believe this feature would reduce eye strain and it would also give fusion a classic look and feel, and also let the user the option of how dark and light they what there UI to be. (Example below)
if this is not possible an alternative feature could be a blue light filter which also reduces eye strain.
For example Adobe CC products -