[E net]

I have both at home an Nvidia Shield with android 6 on my main tv and a couple Mi boxes with oreo on bedroom tvs. I'll test it when I get home. I know for a fact that the voice to text no longer works on the Mi boxes it used to hoping they get that fixed its a pain typing everything out with a virtual keyboard. What type of search are you trying to preform exactly?  A voice to text search from within an addon via virtual keyboard or Googles search to say pull up a movie or show? if a google search it should pull the results from all the apps on the device Netflix, Vudu, Hulu, Starz, HBO, Google Movies and of course Kodi However it only pulls Kodi content if it is in your Library not from addons.  

For example When I want to enter a movie search name which is different to the filename. So from inside the skin I select edit name/sort name the long press the OK key on the remote. This brings up the Google speech to text search. I know this worked in a previous skin. 

OK so I'm not sure if this is Going to help you but if you press the microphone button from within the skin it opens up Google assistant. I just figured out that when using the virtual keyboard if you long press enter on the words English QWERTY it brings up the old voice to text works great try it. 

 I have never used Google Assistant inside a skin, I always press the OK button when I'm actually on the virtual keyboard.. Is that the one you are talking about?