It may have something to do with your internet provider. I changed from Sky Broadband to Virgin (fibre). After I changed providers I could no longer cast my laptop to my Samsung TV. It showed as a device but not a display. After many a frustrating hours trying over and over to connect, I decided to daisy chain my old Sky router to my new Virgin router (you have to log in to your old router and change some settings to make this work).
You then get the Broadband signal passing through the virgin box into the Sky box. You connect both devices to the old router (in my case sky using the old sky password) and then you can cast. So you are essentially using the Virgin signal through the sky router. Then it seems to work fine and it recognises my TV as a wireless display.
So for me at least it seemed to be a Broadband issue stopping this. I think it might be something to do with the 2ghz 5ghz split in the fibre but I am not techy so I don't know.....
Hope this helps some people.
EDIT: By the way, a really easy way to check if this is the issue is use your phone as a hotspot connect both devices (Smart TV and Computer/Tablet etc) to the hotspot. If your computer now finds the Tv as a wireless using the mobile phone hotspot, it is something to do with the internet. I couldn't get the setup to fully work through the mobile but my laptop found my TV which is where I started to realise it must be the internet.
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