My S9 did the exact same thing yesterday. I sat for hours reinstalling the apk and resetting my device. Once I did some deep researching I found a video where the guy shows you what the issue is. So with samsungs last update they released a dummy update which essentially disables the feature until a final update is released. You can see if yours is a dummy update by following these steps. go to settings -> Apps -> Bixby voice -> Mobile data. If you scroll down you will notice that it says Bixbydummy. Also on that page you will see a time frame eg. 1-31 May. From what I understand this date is the time frame of which the next update will be released in.
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