userJTwrM8eYK6 - Go to Settings, then go to Apps, then Apps Manager, click on the 3 dots on top right corner and select Show System Apps. Locate Samsung Voice Input (Should be one with the Microphone icon on it, not the Bixby "B" on it), select it and select Disable.
If the "Disable" button is greyed out, you are looking at the wrong one.
I followed those instructions to a T with no effect on my S8 I just bought last week. I did manage to do what many posters have done and disable it for half a day, but the "accepted solution" here did not work on mine at all. In fact, it's still showing as disabled, but now on texts and email, the big blue bixby screen comes up.
I have the Samsung S7 which does not show Samsung Voice Input as an option. I see Samsung Text-to-Speech engine but I suspect it's not the same thing. After years with Motorola phones, I figured I'd try Samsung & after spending a lot of money on this phone, I soooooo regret that I changed. This voice input is the absolute worst!
Any advice with disabling Samsung's voice input on the S7 would be massively appreciated. I'll get rid of this phone if I can't get Google's voice-to-text back. That's how much I use it.
I did what you said but when I got to Samsung voice input app it had two boxes one said disable which was grayed out, the other said force stop ,since I was not able to disable it, I hit force stop. Unfortunately the Samsung voice input still keeps turning itself on ,when I go to the app now it shows both boxes greyed out the disabled and the force stop box but the app still keeps turning itself on.