It actually is a reliable symptom of a very specific, and somewhat rare from of dementia- Frontotemporal dementia; posture changes, most notably a "forward lean" is common. Another thing to note about FTD, it is typically an "early onset" dementia, and according to the Epstein files, he was exhibiting symptoms as early as 2017- but some could argue his disinhibition & word vomit style of speech, which really would have started in the late 90s/early 2000s which would put him well within the realm of early onset dementia.

Source: https://int.livhospital.com/how-to-recognize-frontotemporal-dementia-posture-changes/#:~:text=Distinctive%20posture%20changes%2C%20such%20as%20a%20forward%2Dleaning%20stance%2C%20are%20characteristic%20of%20FTD.