Any TVs which come with Google TV as an OS have an option at first startup to be set up in "Basic Mode" which allows it to basically be used as an HDMI monitor. The main TVs which ship with Google TV are Sony's.
We have a mini PC dual booting Fedora and Windows plugged into a Sony TV. We only have Windows because some services such as Netflix purposely only allow 4k streaming on the Windows Store app. We also have a 4k Blu-ray DVD and CD player because we like to own physical media.
This setup has worked great for us. A good resource for this stuff is r/HTPC. As far as I know, we don't have any downsides to doing this as opposed to using the smart TV itself. Both the Windows and Linux have good support for surround sound (we have a 5.1 setup), and for HDR content we can use windows.