I previously used my PS4 for watching everything, but having a full desktop OS is just way better: I can browse the web on my TV, control it remotely with my laptop's keyboard and mouse using Barrier, open multiple live feeds in picture-in-picture mode, play music in the background of whatever I'm watching, etc. Also, when I'm watching sports and they go to a side-by-side commercial break, I use the zoom accessibility feature to zoom in on the tiny live feed so I can watch that full screen without seeing any ads haha.
I'd be curious to know more about how you configured KDE. I run a pretty vanilla Pop OS setup right now, which is more usable than I expected with my USB remote, but I've been meaning to explore how to set up something more "smart TV"-like that's a bit easier to navigate. My initial thought was to write a browser extension or a custom app with an embedded browser, but that feels like a bit too much work for something that's supposed to be a leisure/entertainment setup.