You didnt mention your Roku model #s: Settings/System/About
This is important, because Peacock TV has model restrictions:
Roku 2 (4210X model only)
Roku 3 & 4 (model 4200X or later)
Roku Streaming Stick (model 3600X or later)
Roku Express/Express+ (model 3900X or later)
Roku Premiere/Premiere+ (model 3920X or later)
Roku Ultra/Ultra LT (model 4640X or later)
Roku TV and Smart Soundbar (model 5000X or later)
Adding it via device or via the browser wont make any difference if your models arent supported.
FYI, Factory Resets dont remove apps from the account (apps are account associated, not device associated) - the apps will be restored once you re-activate your Roku.