Is it possible to cast from Dell laptop to apple TV

Officially that is not supported.

Unofficially, there are a few third party software vendors that offer some sort of AirPlay-like functionality. Search ‘AirPlay for Windows’.

Alternatively, you may use Home Sharing, which is supported through the iTunes application. Home Sharing lets you access compatible media files through the Computers app on the Apple TV box. (Useful for local files, not for direct web access.)

Yes I use Plex app to do that. Download the Plex app to your AppleTV (you need at least AppleTV 4/HD) and setup the Plex server on your Win 10 PC. https://www.plex.tv

As was already said there is no official way to do this though. iTunes home sharing also works and is a little easier to setup than Plex.