I was just trying to get this working as well. I connected to my TV using KDE and audio came through, but I didn't find any sort of screen mirroring. I'm not sure how up to date the info is, but I did read that KDE Connect comes with Miracast built in, so if you have access to that it should be an option.
Unfortunately, my TV is an old 2018 Samsung 4k, so I have no access to Miracast to check, so I didn't dive far enough into it to know for sure. My solution is probably just going to be setting up a Raspberry Pi media build to the TV.