When the TV was new, we could activate google assistant by speaking to the TV set.

Now, it will only activate google assistant if we press the assistant button on the remote.

Nothing has changed about the TV setup.

The MIC LED indicator is on.

Troubleshooting:

Tried the command words in a quiet room.

Reset the TV

Changed the TV position (wall vs table) per the Sony Troubleshooting instructions

Toggled the Google Assistant on and off

Checked that the device is logged into a valid Google account.