Very few computers have video inputs, and those that do are almost always analog connections. There certainly are USB devices that add video input to a computer. I have one on my computer for copying old family VHS tapes to the computer. But since one of my computer monitors is a 43" 4K Roku TV, it really isn't necessary to send anything from a Roku player.

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But if you are referring to sending whatever the Roku is streaming to a computer over your wireless, then DBDukes offered the correct answer. Nope, can't do it without spending lots and lots of money on hardware. And I mean lots.
Dan
Roku Stick (3600), Ultra (4640), 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.