I installed non google keyboard and voiceboard, apps I can use, but each time I turn the device off, I’m prompted to use google’s boards and asked to say something.
Are you sure you’re turning the device off? More recently Android has switched to open the Google Assistant upon holding the power button.
The “new” method to switch off your device is to press the power button and volume up at the same time.
You can switch this back in the phone’s settings though. I’m on Android 13 with a OnePlus 11 and it’s under Additional Settings -> Power Button -> Press and hold the power button.
Or just search for power button. Search is nice.
Wow, that’s beyond dumb
DId you already try disabling google board using ADB?
OTOH, you may simply activate airplane mode, instead of switching the device off. Battery consumption in airplane mode is close to 0.