A year ago when I received my 2016-vintage Roku Ultra, I set it up in my home theater room, well off to the side of all the other equipment. I connected it to my WiFi router on 5gHz. The Roku and router are about 10 feet apart with one otherwise empty wood-stud-and-drywall wall between them. The Roku said the signal strength was "excellent". I checked the signal at the Roku with the WiFi analyzer app on my phone, and it concurred: very strong, clean signal. Be that as it may, the Roku would simply drop the connection from time to time...and far more often than was reasonable. I had updated the Roku's firmware when I first turned it on, yet, even after I reconnected it to my 2.4gHz WiFi, it would not maintain a reliable connection. My cable provider technician was visiting for another, unrelated, issue so I brought up the Roku's problem. He went out to his truck and came back w[color=#1c1c1c][font=Noto Sans, Helvetica Neue, Segoe UI, Helvetica, Verdana, Arial, sans-serif]ith a small cardboard box, which he handed to me while saying "try these". Inside the box were two white-wall-cube-type thingies. They each had some L.E.D.s and an Ethernet jack on them. You plug one into a 120V outlet near your router, and then connect the cube and the router with an Ethernet cable. Then you do the same with the other cube near your Roku, connecting the Roku the same way. This gives you a reliable Ethernet connection between your Roku and your router. I checked the connection strength between the two cubes using an app provided by their manufacturer, They're good for between 600 and 850 mps in my location, which is WAY more than I need. That was the end of my connection problems with my Roku Ultra.
It has been perfect for over a year now, which is why I purchased another pair of the "cubes" (they are sold in pairs) when we bought our new TCL TV this Christmas. Before I ever turned on the TV, I connected it to an Ethernet "cube" (apparently, once your router is connected to your house's wiring with a cube, you can have a total of 16 cubes connected on your "home network"). When I then turned on the TCL for the first time, the internet connection was already "hot" and I proceeded to update the firmware in both the TV and the built-in Roku. This connection is on another floor in our house, so I again checked the connection speed, which was around 350 mps...still a good 20 times what I would need to stream 4k.
I know you don't want to hear that your Roku TV has an unreliable WiFi system, and maybe it actually doesn't...maybe there is some other extenuating problem, unrelated to your TV's Roku/WiFi, that's causing your connection problem. Heck, I still don't know what the problem was with my own Roku Ultra, but whatever it was, it was rendered moot when I bypassed the whole RF connection issue with these Ethernet wall cubes. So, if you can't solve your connection problem, I just wanted you to be aware that there is another, iron-clad, solution that's available to you...[/font][/color]
Sorry about the weird character string in the first paragraph...I don't know what happened, but it's my first post here.