I don't have Android 9, but if some of the notifications are like on Android 8, then you can try the following:
Open Settings -> Apps & Notifications. Click on "See all apps", then the 3-dot and select Show system apps.
Look for Download Manager, click on it.
Click "App Notifications" or "Notifications", then disable "In progress"
Note: You may find 2 ...
Pico TTS is unmaintained and dead. At least publicly. Presumably, the fixed version of it is what is now called "Googls TTS", which is no longer open source.
My suggestion, if you're looking for an open source TTS, is to use Flite TTS, which is available via F-Droid repository or from github.