The fear is that the TV will still be annoying, with popup menus and "Oooh! No WiFi! You need to fix this!" alerts.

A “normal” tv doesn’t need a wifi password ;)

Just as long as you never have any guests that want to be helpful and connect it to the Internet either via your guest wifi or their own phone's hotspot so they can watch their Netflix or whatever on it.

Or you accidentally connect it to your streaming box (Apple TV, Roku) with an HDMI cable with Ethernet:

* https://en.wikipedia.org/wiki/HDMI#HDMI_Ethernet_and_Audio_R...

The streaming box will have to be complicit and act like an ethernet switch or NAT router (in case of Wi-Fi not supporting WDS so can't be bridged) to passthrough the connection.

There's no reason to believe this won't be a configurable option on the box itself, but this is a moot point because I have yet to see anything in the wild actually supporting Ethernet over HDMI.

They soon will be able to connect to your neighbour's wifi via Amazon Sidewalk

This gets raised all the time but I just don't see it being necessary - the vast majority is happy to voluntarily provide it with an internet connection. The ones like us who fight it is a very small minority not worth spending on including modems/Sidewalk/etc in every TV.