We've had formant synths for several decades, and they're perfectly understandable and require a tiny amount of computing power, but people tend not to want to listen to them:
https://en.wikipedia.org/wiki/Software_Automatic_Mouth
https://simulationcorner.net/index.php?page=sam (try it yourself to hear what it sounds like)
I know there will be some smart arse out there saying "Just install Linux" Pleas don't I have to use a screenreader called NVDA to read the screen to me as I am blind.
There is a screen reader in Linux but it just is not that good. If it was better then I would think about it. I have tried!