But there was a WiFi option in the settings previously when you connected it to WiFi so I can't understand how the option would disappear from the TV menu.
You'll be better off with the Ethernet connection anyway, so just disregard the WiFi.
My Apps on my old Smart Sony TV ceased to function a long time ago and the only way of getting some of them back was by resetting the TV which was a pain in the proverbial and anyway they couldn't be downloaded but were fixed.
I ended up buying a Roku device and plugging that into the TV via a spare HDMI socket. That connects easily to my WiFi and is so reliable and much easier to use.