Roku remote for LG ThinQ TV

Hi! I'm looking for advice on how to set up my new LG ThinQ TV such that the remote for my Roku Streaming Stick 4k will be the only remote that I need to use (turn the TV on, navigate the Roku screen / apps, volume, and turn the TV off.

I currently have another LG Smart TV and the above is how that one is set up. Moreover, my new TV is a replacement for another LG Smart TV, and the above is how that was set up.

Now, with this new TV, I have to turn it on with the LG remote, navigate to the HDMI input tile (in this case, HDMI 2) and select it. The Roku screen appears, but the LG remote can't do anything with it. So i then pick up the Roku remote, and can navigate the Roku screen.

I spent several hours on the phone yesterday, talking to LG support, Roku support, Best Buy, and even my internet service provider. All the device-related settings (for the TV and for Roku) are set up as I was instructed. And, while i was on the phone with the Roku support, it worked as described above. We even turned off the TV, waited a moment, turned it on again, clicked around the apps on the Roku screen, and i selected one to make sure it worked...and it did. Alas, that success was short-lived, as it once again reverted to requiring that I use 2 remotes.

Any advice to helping me set this up so I only need to use 1 device for power (on and off), navigating the Roku screen, and volume) would be greatly appreciated. Thank u!!!