Wondering if you tried sampling / adding a voice that’s not already on your Mac, or voices from other countries.
If you have already looked through these, please excuse, and check out the linked articles at the bottom...
Apple menu
> System Settings, then click Accessibility
in the sidebar.
- Click Spoken Content on the right.
- Click the “System voice” pop-up menu, then choose Manage Voices.
- Find a voice for another language: Click the name of the language in the sidebar. (You may need to scroll down on the left.)
To show more voices for the current language, such as for another country or region, you may need to scroll down on the right.
Sample a voice: Click the Play button
next to the name of the voice.
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There's a (non-Apple) article online from 2021:
2 Black American Siri voices included in new Apple iPhone update
https://thegrio.com/2021/04/27/2-black-american-siri-voices-included-in-new-apple-iphone-update/
or
Check out the Siri Voices for Americans on Mac: Apple menu > System Settings > Siri > Siri Voice > Select
(Am using an earlier MacOS than you, yet the American Voice 3 there, sounds like a female voice that may suit.)
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On this (non-Apple) site you can hear "Tamira" an AI voice that may be what you are looking for:
article is also from 2021
https://www.acapela-group.com/news/african-american-english-digital-voice/
There is also a "type and talk" demo web-page, where you can test their other voices with your own input:
https://www.acapela-group.com/demos/
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If you use Apple's VoiceOver (eg: for screen-reading) you can:
Change VoiceOver voice settings on Mac - Apple Support
To customise voice settings for your default language and additional languages, open VoiceOver Utility (press VO-Fn-F8 when VoiceOver is on), click the Speech category, then click Voices.
When you install voices that are compatible with macOS, they are installed in /Library/Speech/Voices so they are available to all users of your Mac.
More info: VoiceOver User Guide for Mac - Apple Support