After playing with this for a while now I see 3 ways to fix it.
Roku did this a few years ago with getting rid of downloads and things as well, they never notified anyone and played dumb until people forgot about it. First, lets deal with reality. Lipstick on a pig. Roku is the same as a $50 Android box on Amazon except with Roku you cannot download whatever you want to it. Yes the box is bult in to the TV and it tells the manufacturer OS to boot directly to it. It also charges monthly fees 5 times the price and is very limited on content. Good idea but they have closed vision and their mindset on larger things like taking over Google Home that will destroy the company. They stepped over a $100 bill to pick up pennies. The Good part about it is that you don't have a separate box to plug in to HDMI 1 so that it turns on and off with the TV. Now you can put a sound bar in to your HDMI1 port that turns on and off when you turn your TV on and off. Sound bars are Google compliant now as well and easy enough to set up a routine, so Roku has once again shot its in the foot with it's closed view of reality. Very poor management. Oh well, it is what it is. The problem here is the pig with a bit of lipstick thinks it is now Miss America and has blocked everything outside of Roku thinking its customers will change out all their lights, alarm systems, window shades, plugs, Google Homes etc. because they were able to change a few start up screens and then overpriced their monthly fees on a $50 Android box. It's comical but sad that they are losing customers daily so they now try to force people to switch to them. Welcome to the world of textbook management who are blind to the updates in technology around them and have no clue to their clients. Simple fix to where they could do well but are too busy cheating people than to take a serious look and adjust their business. The older sets still work if you installed Google and other software on them previously. People say no, but they do and the updates do not affect them because people paid for some of the software and it would be illegal to not allow them to use it, Roku has to live with it until those sets **bleep** out and people replace them. In truth it is illegal to do what they are doing now by saying they are compatible and then blocking Google Home and things when advertising that they do work with it. I see a class action or full revamp of the company or a buy out or bankruptcy in their future. The world is all about lying to people now of days with all the filters to make people skinnier or look prettier and Roku has decided to jump on the bandwagon instead of being a respectful business. Lipstick on a pig and lying about the truth telling people they are Miss America is how they are dealing with it. So how do you get around it and use voice to control your TV, this is what I have found. Like I said, my old TV's work without issues so, it is only the newer ones.
1. Return the TV and get a Google TV. This is what I did but only after finding the solution just because screw them. I also emailed the the president of Roku and the TV manufacturers to notify them of the false advertising claims they are making on their packaging.
2. Get a voice remote. 30 bucks online but then all you have to press the mic button each time. PIA but works
3. Get the new Pro remote for 80 bucks that is always listening and you can say Hey Roku <command> instead of Hey Google <command>. Original thought by Roku, I think not.
That is the options going forward on Roku
In the end, if it's a new TV because the old ones do work with Google and you cannot return it, I would recommend going on Amazon buying a Google plug, an Android box, connect it to an IPTV service for $10 per month with thousands of movies and channels and connecting it all to Google. If you get the more expensive Android box ($100-$200) it will just be plug and play with voice and everything already setup then add your $10 per month subscription and you got much more than false advertising lipstick on a pig, you will have a separate box though.