If you search the Internet for "windows can't duplicate display" you'll find plenty of people with the same issue you're describing going back years. I don't think it's the TV, although I did find one person that had to turn off "theater mode" on his Sony TV to get his display to duplicate, so I suppose it's possible that there's a TV setting that affects it.
I can hook my laptop to other TVs and monitors that are not the Roku TV and they work just fine, it's only when I try to hook my laptop to my Roku TV that this issue happens.
I went to 'Settings', then 'Display' then scrolled down to 'Multiple displays' and chose 'Duplicate these displays' it went back to normal. Not sure how long it will last though, but it did go back to normal.
