How to fix broken text to speech rate on Big Sur I'm on macOS 11.2 using a 16 inch 2019 MacBook Pro. I noticed when I use the text to speech functionality (system preferences &gt; Accessibility &gt; spoken content), the Siri voice doesn't adjust it's speech rate when using the slider (or the button on the popup controller). One thing I've noticed is that any other non-siri voice works. Furthermore, the voice was working till I reimaged my computer. Lastly, I have an older mid-2015 mac and it works just fine (even after I completely wiped it).
I tried to copy over some plist files from my old mac to see if I could get that to work, but that failed.
Any suggestions on how to fix the broken functionality?
Well, it looks like it is a regression from macOS 10 to macOS 11. I confirm your saying, it worked and now Siri's voice speed can't be controlled anymore in Preferences Pane &gt; Accessibility &gt; Spoken Content
Apple does not notify anything about it in macOS 11's doc
The feature seems to be broken and bugs about Spoken Content are not new on MacOS. Look at this for instance.
Unfortunately, I think your only option is to open a bug ticket on Apple's website and wait until enough people are complaining about it to get it fixed.