Hi Josiah Burden,
Good day. I'm Jhun an independent advisor. In regards with your issue, unfortunately, reading with Amazon Kindle Cloud Reader via browser is messy, and many TTS tools don't reliably work yet.
The official Kindle Cloud Reader via web/Edge/Chrome and most Kindle apps do not support built-in-text to speech.
As a workaround, on Windows computers you can use Kindle for PC combined with a screen reader, to read aloud Kindle books.
I hope this helps.
Regards,
Jhun