The ability to enable seconds on the tray clock was one of those legacy features Microsoft dropped when developing the initial Windows 11 release, contributing to the overall negative reception of the OS and its fancy yet slightly crippled taskbar. Luckily, one of the recent updates brought the much-needed feature back, and now, Microsoft is changing its location.
Quietly and without any public announcements, Microsoft updated the recent Windows 11 Insider Preview build notes. Multiple posts now have a new change that notifies users about a new place for the "Show seconds in system tray clock" option. Stable Windows 11 builds have it under Settings > Personalization > Taskbar > Taskbar behaviors, but the recent preview builds moved it to Settings > Time & Language > Time & date under "Show time and date" dropdown, which arguably makes more sense. Also, you can always use Settings search to find the needed option.
Here is what Microsoft added to the release notes:
[ADDED 7/29] The setting to show seconds in the system tray clock has moved to Settings > Time & language > Time & date under “Show time and date in the system tray”.
Despite the new home, the feature still warns users that toggling on tray clock seconds causes the operating system to consume more power. About a year ago, we ran a small experiment, which proved the claim to be true—turning the feature on results in about a 1.9% battery time reduction.
The tray clock seconds feature is one of those capabilities that previously required messing around with the registry to turn it on. In Windows 11, Microsoft finally made it much simpler and user-friendly. Now, the company is doing the same with the ability to disable mouse acceleration and change the scroll direction. Those options are finally available in the Settings app in the recently released Windows 11 preview builds. It should not take too much for those things to show up in stable builds.