Is there a feature or plugin that will display all my hotkeys, categorized & searchable?

... Something I can pull up fast with a hotkey and search to find the hotkey I forgot?

... And something that auto updates when I changed hotkeys?

That would be almost impossible, simply due to the amount of shortcuts already in use. But you can find all the shortcuts in the System Settings -> Workspace -> Shortcuts section, where you also would create or change shortcuts anyway.
In KDE applications per app shortcuts are directly available in the App Menu with

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 Ctrl+Alt+,