This is done by a firmware update
Nikon has released firmware updates for the Nikkor Z 20mm f / 1.8 S and Nikkor Z 85mm f / 1.8 S lenses for Nikon Z mirrorless cameras. In both cases, the update is version 1.01.
Nikon fixes a bug in Nikkor Z 20mm f / 1.8 S and Nikkor Z 85mm f / 1.8 S lenses
The description of the firmware version 1.01 says that the update fixes a single bug. This error is manifested as follows: During autofocusing, the display momentarily becomes brighter and the aperture display changes to “F–”.
Updates are available for free on the manufacturer’s website: Nikkor Z 20mm f / 1.8 S, Nikkor Z 85mm f / 1.8 S.
