I’ve setup my Wifi router with timed access. This allows internet for certain time slots and denies access outside these time slots. After installing iOS 14 on both my iPad and iPhone I noticed no internet for me too. But I have my own rules based on the MAC address of the devices.
Turns out there is a Private Address option (enabled by default) that spoofs your MAC address to reduce tracking across different Wifi networks. I had to turn that off to get internet. Here is where you can find it. Go into settings > Wi-Fi and press the little i after the Network to get to the page in the screenshot. If you flip the switch on Private Address everything is alright.
Seems to be a feature not a bug: https://support.apple.com/en-us/HT211227