I think you could check out this post I've linked below! It goes over 3 different TTS options (1 for Windows, 2 for Android):
$1I have been using the (free) apk linked in the Github in the above post, and just some things to note: 1) I find the voices are great at intonating, which has been helpful for my comprehension of written works, 2) the app is passing data onto Microsoft if you have concerns about that, 3) if you don't understand Mandarin, you might have to click around on different voices and buttons before you figure out what's going on, and 4) in my experience, it seems to require use of Wifi to run the TTS---I can't get it to work on data. Also, some voices don't seem to work. I've settled on using the voice Aria in English.
Another option I've used, which doesn't require the same Network permissions that the aforementioned apk asks for, is RHVoice:
$1. I run it on Android offline, and it's worked for me for a couple years. It runs well when coupled with Librera Reader:
$1