Yeah just learned this from trial and error after getting a new router that supports WPA3. I have a UN43TU8000FXZA (aka TU8000) model and it's the same problem. The weird thing is the encryption setting says WPA2/WPA3-Personal. So it's backward compatible. I can't seem to find the wireless security specification for the TV anywhere but it makes me wonder if the TV is using WPA?? That's...very old.
EDIT: Alright I was worried for a bit but I worked around the problem by leaving my main Wifi network configured with WPA2/WPA3-Personal (still think the TV should have been able to connect to it, but whatever...) I enabled the guest network and turned-off broadcasting the SSID. So basically, a hidden network exclusively for devices that have trouble connecting to the main SSID. I set the hidden network to use WPA/WPA2-Personal and then manually added the network to the TV by typing in the network name and chose WPA2AES as the security mechanism. This is an acceptable setup for me. Strangely, when I went through the manual setup on the TV I saw an option to use WPA3-Personal which I gave one last try but alas it didn't work.