What I use is the Apple TV 4K unit. It costs close to $200 sometimes cheaper and cable internet has a special now as a freebie incentive.
you could also look in the owners manual for your new tv at the manufacturers web site which may have a work around.
How do I project content from my iPad, MAC or iPhone to my LG TV? I used to do this with my Sharp TV but won't work with LG TV
Is your LG tv Chromecast enabled? What content are you trying to cast to the TV? You could use most screen-mirroring software if the TV has built -in mirroring capabilities like my Sony TV. You could also buy a Chromecast device, or a Roku stick a LOT cheaper than an Apple TV, but not all content is allowed to be shared this way.