Hello All, I recently bought 65S425 and just got my hdmi cable upgraded just to get the 4k to work. My graphic card is a radeon hd 5450. I setup my hdmi input as a computer and set it to hdmi 2.0 input. I restarted the TV per some suggestions and got the most recent updates on roku side as well. I can get 1080p with 120hz to work without a problem.
Thanks for reaching out. I'm not quite sure what issue you're encountering, but that model of Roku TV is not capable of 120Hz refresh rate. That may explain the issue you are seeing if you're trying to send that signal format. I'd recommend contacting your Roku TV manufacturer for more information about the specifications of their TV and any other questions you may have. You can locate TCL's contact information here: https://community.roku.com/t5/Manufacturer-Support-Warranty-Resources/Contacting-Support-for-Your-Ro...
I connect my work laptop to my Sharp 4K Roku TV, and get 2160/30 without an issue. I can't say if my laptop is capable of 4k/60, but my guess is it's not supported. It's a workstation with a Quadro video card, not a media player. But for my purposes (teleworking) 4K/30 is more than enough. If it's 4K/60 you're trying to get, I don't think that card supports it. From what I could find online, it supports DVI: 2560 x 1600 / VGA: 2048 x 1536. I have the same card in my HTPC, which is mainly used for OTA recording, not video playback. I just checked and it's only reporting 1920x1080, and it's connected to an HDMI 2.0/4K AVR and TV. That is a very low end video card, and just can't support that resolution.
Dan Roku Stick (3600), Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.