Quickly off the top of my head it would be completing all secondary objectives.
I can't remember if data pack things contribute anything to additional completion status.
The current any% run just does the basic primary objects iirc
I've set 100% as getting 5 Stars on every mission as it makes the most sense. There's four in-game requirements to get them:
- Beat the mission under a certain time
- Complete all secondary objectives
- No reloading from saves
- Play on Commando difficulty
It may or may not require 5 stars on all four categories to have 5 stars overall. I'll check this when I can. If it doesn't, the definition could be changed to 5 stars on everything (since that would fit '100%' better). Depends on what the runners think.
I noticed something while watching some runs. Even if you reload from the auto-save at the start of the mission, it still counts it as a reload. Does using the restart button do the same?