Have you looked at this add-on?

https://addons.thunderbird.net/en-US/thunderbird/addon/categorymanager/

The Cardbook add-on also manages categories.

I have, but it adds an additional layer of complexity just to have a category. It doesn't have the same simplicity and has to update the information which may not work with iphone or android when syncing. Is there an email to contact the developers of the Thunderbird Software?

Thanks :-)

Implementation of categories is discussed here: https://bugzilla.mozilla.org/show_bug.cgi?id=1764184

Thank You. I have seen a multitude of people talking about this. Is there a way to contact the developers directly as opposed to creating concerns and replying back and forth to people who aren't responsible for actually implementing the request?

Thanks :-)

Since there is already categories available for both calendar & task entries, why can't they make it available for contacts which needs categorization more than calendar & tasks. Why hasn't' this update been implemented in-spite of several years of inquiries?

I don't know who is responsible for Address Book development, and I expect that trying to find that out will be a fruitless endeavour. Perhaps try to contact one of the developers of the add-ons mentioned above as to why categories aren't available for contacts. Or, post comments in the Bugzilla bug.