Why won’t my Apple TV connect to my new Wi-Fi network?

1. Try the steps as mentioned in: If your Apple TV can't connect to Wi-Fi - Apple Support
2. Try the ‘Other…’ option instead of selecting a listed discovered network. Especially if the password has been changed, but not the network name.
3. For Apple TV (4th generation or earlier), verify that the router or access point isn’t set to use WPA3, as only device models from ~2018 or later support that. Instead use ‘WPA2/WPA3 Transitional’. Some users report that they had to set ‘WPA2’-only first.

I think (3) will be the solution, though.

On your ATV if you go to Settings > Network > Connection > Wi-Fi is your ATv trying to connect to the old network? If it's trying to connect to the old network delete it by clicking on your (old network name) > Forget Network then choose the new one you are trying to connect to.