My source for this was watching the final myself. When I watched the broadcast myself it was clear to me that this was the problem. Also the (Finnish) commentators were very knowledgeable in the sport and pointed out the problem many times.
I was unable to find a clip of his throws in YouTube, but here's a Google Translated article from a Finnish newspaper: https://bit.ly/3xvZWMk.
But it has been close? Johannes Vetter got a result of 97.76m under a year ago, that is only 0.72m shy of the world record. Also the reason he was underperforming in the olympics was that the surface of the run-up track was not able to take his weight on the final step and he would slip, making it impossible to perform on his normal high level.
I was unable to find a clip of his throws in YouTube, but here's a Google Translated article from a Finnish newspaper: https://bit.ly/3xvZWMk.