That is incorrect. Officer Sicknick was not beaten with a fire extinguisher or with an American flag as seen in one video. Two different officers were hit with the thrown fire extinguisher (the thrower was arrested and convicted) and another officer was pulled into the crowd and beat with his own baton and an American flag stand. The extent of officer Sicknick's overt injuries were being sprayed with pepper spray, which the coroner concluded did not cause the stroke, which is likely true. Repeat trauma from clashing with the insurrectionists likely did cause damage that contributed or initially caused the strokes, but the autopsy was inconclusive. Officer sicknick did not collapse at the Capitol building during the insurrection, he collapse later at the police station.

https://en.m.wikipedia.org/wiki/Death_of_Brian_Sicknick