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.

you can still find some dumb displays if you search for "monitors" rather than "tvs".

Projectors are another option

Wal-Mart's Sceptre brand still sells a wide range of dumb TVs. Not super great performers, but also not expensive by any means.