Hello everyone i have a ONN Roku Tv that i am trying to Screen Mirror using miracast on my desktop. My desktop and tv are on the same network. My desktop does list the roku express in the list of wireless displays. When i attempt to connect to the roku it says follow instructions on my device. But nothing comes up on the tv. Ive tried changing the roku settings to prompt and always allow but neither works. the airplay from my iphone works perfectly fine just not desktop-roku connection
Miracast doesn't work on a computer that does not have a wireless connection. My desktop computers do not show any external devices that I can project to, but my laptop shows all my Roku devices, along with smart TVs and my Shield players.
Since your desktop is showing the Express, it must have a wireless card. But if you're using a wired connection for the desktop, that might explain why it won't connect. I've never tried one that way. My laptop is able to screen mirror just fine. All Windows computers are on the latest version of Windows 10.
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Rokus support "screen mirroring" in 2 very different ways:
1) Miracast-based: (Settings/System/Screen Mirroring) - this is coded by Roku and maintained by Roku
2) AirPlay2-based: (Settings/Apple AirPlay & HomeKit) - this is coded by Apple and maintained by Apple
These are two completely different sets of mirroring functionality and do not overlap any code or share any settings - this is why one can work without issue and the other can be problematic.
Also, you mention an "ONN Roku TV" but then you mention a "Roku Express" - its not clear whether these two devices are both yours, or you named/renamed your ONN Roku TV to "Roku Express", or you are trying to connect to someone else's device.
Since you mention nothing ever comes up (on your ONN Roku TV?) when you attempt to connect to the "Roku Express", it suggests that you are attempting to connect to someone else's Roku.
(This is actually very common in dense neighborhoods because the Miracast screen sharing relies on WiFi Direct Peer-2-Peer technology for search & discovery, which effectively means any nearby Roku or other Miracast-based equipment will show in the list, whether or not they are connected to your SSIDs)
Regardless, make sure you:
1) leave the Miracast-screen mirroring mode setting at "prompt",
2) reboot any/all devices (Roku TV/player and PC), and
3) try switching the either the PC or the Roku TV (dont know the TV or Express model, if its yours) connection from 2.4Ghz to 5Ghz, or vice versa (you should have separate SSIDs for 2.4 and 5Ghz if your AP/router/gateway/modem supports dual band)