One of the attractions that did not open with Walt Disney World when it reopened in July was the Tomorrowland Transit Authority PeopleMover. However, unlike other attractions like Primeval Whirl and Rivers of Light, which are now closed forever, this attraction is expected to reopen at some point, and Disney officially updated its website back in August to say that this attraction will be under refurbishment at least through to the end of October 2020.
However, it looks like whatever tune-ups or improvements are happening behind the scenes will take a little longer than expected as Walt Disney World has updated its official calendar and this closure is now expected to last until December 26, 2020, almost a month past the previous extension, which brought the refurbishment's end to November 21, 2020.
Of course the Tomorrowland Transit Authority PeopleMover isn't the only attraction at the Magic Kingdom currently under refurbishment as The Liberty Square Riverboat and Tom Sawyer Island at the Magic Kingdom are both currently closed for refurbishment and will remain unavailable until at least early next year. We don't have any information about what it going to happen during these closures, but we'd guess that the Rivers of America are probably going to be drained as part of this closure, which is why both of these attractions are closing at the same time.
In addition Disney filed two permits for updates to be made to Big Thunder Mountain Railroad that mentioned labor, material and/or electrical for construction to be done at some future date, which has led many to believe this attraction will be closing for refurbishment sometime in the near future, though no dates have been formally announced yet.