History of Blindspot

Blindspot is a triumph: select the Blindspot modifier and complete any activity with grade A or higher.

How to complete

The game text points to the The Portal activity-customization system from Destiny 2: The Edge of Fate, where modifiers are chosen from tabs such as Player Stakes, Faction Drop and Minor Negative Modifiers. Game Rant's guide says the Equipment Locked modifier (x5 challenge multiplier) is the easiest route to an A grade; combining modifiers that raise challenge multiplier is how grade is raised.

Unconfirmed: none of the pages I opened describe the Blindspot modifier itself, so what it does and where it appears is not verified. Check the in-game modifier list.