I've found this to be harder than it seems.

I had a tesla gen3 wall charger. I updated it and .. crap ... it created a wifi access point that I did not want and would not go away.

so I decided to disconnect the external antenna. unplug the mmcx connector and easy peasy disconnected.

...and the wifi board switched to its internal antenna which was just about as strong.

so I thought... Hmmm.. maybe I can add a dummy load. I wired up an mmcx->rp-sma wire plus a dummy load.

same thing. It may choose the strongest input? or do diversity?

I've now been thinking of downgrading the firmware.

For the most part, don’t connect to Wi-Fi and use hdmi in. If you’re one of the lucky few with a tv that will wardrive your neighborhood looking for open networks, find the Wi-Fi chip and pull it off.

I find it easier to start with a dumb device. However as that increasingly looks not so possible for TVs, I'd love to see somebody document the process for what you propose.