I bought an USB type C to HDMI adapter to transmit my Samsung Galaxy S8 screen to the TCL Roku TV, since the wireless cast is not working good. It didn't work, the customer support says that the adapter only works for 60hz refresh rate and my TV is 120hz.

I tried the adapter in another old cheap TV and it works good so the issue is the TV refresh rate.

What can I do? Since wireless casting is not an option (don't know the reason why my phone disconnects like every 5 minutes or less) I don't have wifi in my area or unlimited data, that's why I thought the cable was a good plan.

Not sure why your S8 can't screen mirror. My S8 works fine with my Sharp Roku TV. I installed the Smart View app on the phone and it works fine. Have you tried that?

That app was installed by default. I use smart view but it works for like 5 minutes or so and got disconnected. That's the reason I bought the adapter but it didn't work either.

Perhaps the difference for me is that both the phone and the Roku TV were on the same network, the phone via WiFi and the TV hard wired to my network. But I didn't have any disconnect problems.

I tried today but in a different TCL Roku TV. It worked well, I think the problem is that I use smart view without a router, only with my wifi direct.

But I haven't solved the hdmi adapter issue..