I watched the summer riots on youtube live streams, I don't recall the FBI using this technique for the tens of thousands of man-hours spent looting, burning and rioting in Portland, LA, Seattle, Minneapolis, Chicago, NYC or Atlanta.
Its definitely the FBI's job to figure out who breached a federal building, let alone the seat of our legislative branch during an active session.
That being said... the FBI, DOJ, DHS, and state agencies definitely do shady stuff and track people via their devices at protests. I'm remembering surveillance planes over Baltimore that were traced back to feds.
https://theintercept.com/2020/07/09/twitter-dataminr-police-...
Know where I recalled I read this? Here.
https://www.cnn.com/2020/07/28/us/umbrella-man-associated-wh...
Maybe they used the same techniques there. Does that make you feel better?