Add am/pm after the 12-hour clock time in the status bar
It is possible only if your device is rooted and cannot be achieved on stock devices. Changes to status bar components like the clock, date, battery icon, percentage, etc. require root or a custom ROM
On rooted devices, one way is to install Exposed/EdXposed framework and Gravitybox module (For Android 10, see How to install EdXposed on Android 10 without triggering safety net)
Note that Gravitybox does not play well with heavily modified UI, so it's better to check in device/Gravitybox threads on XDA