Roku ultra, Samsung qn90a and Sony str dn1080

Dumoch126Using an AVR as the 'control center', plugging the TV and Roku into the correct HDMI port will give you the ability to use the Sony for both audio and video providing you've studied the manual to find the correct ports.

Using an HDMI 2.1 cable, plug it into the Sony's TV port, and the other into the TV's Audio Return port. Then plug the Roku HDMI cable into the correct port on the Sony (check the manual to learn which is best) and plug the AC adapter into a power strip. Depending on the Roku model, its unlikely you'll be able to control the Roku with the Sony remote since most Roku remotes use WiFi direct. If you want to control the TV power with the Sony, study the manual to learn how.

Prior to tuning the Roku on, set up an account on the home page: https://www.roku.com/

I'm going to assume you know how to set up the Sony for use with the TV, so you you'll use the Sony remote to select the HDMI port for the Roku. Then using the Roku remote, you'll be directed to log into the WiFi network. Once logged in, if the Sony supports 4K HDR and Dolby Vision, select THAT display setting on the Roku; if not, use 4K. For audio, select 'Auto' for Dolby format and 'Pass through' which will allow the streaming channel to 'pass through' the native audio format for each channel. The other settings are self explanatory