First try moving the mouse pointer into the top-left and top-right corners of the screen. If the "P" appears, you may have enabled the preferences option to "show 'P' only when pointing into the corner".
When the "P" in the menu bar does not appear, PopChar is probably not running. Locate the PopChar application icon in the Applications folder and double-click it. See the next section about how to make sure that PopChar automatically launches when you start up your computer.
PopChar Not Visible in macOS Tahoe?
In macOS Tahoe, Apple introduced a new setting under the Menu Bar section of System Settings. If you notice that the PopChar icon is no longer visible in your menu bar, don’t worry—it’s just a setting that needs to be adjusted.
Here's how to fix it:
Open System Settings.
Navigate to Menu Bar > Allow in the Menu Bar.
Locate PopChar in the list.
Enable the toggle to make the PopChar icon visible in the menu bar again.
Once you turn this on, PopChar should reappear in your menu bar as expected.