I haven’t seen this (as I’m not close to re-registering), but it shouldn’t be that there is no way to close it or continue the process to re-register the free version. If you can try it again and post a screenshot of the window it would be helpful.
Cloud services are really just emergency updates to provide you with the latest signitures quicker and the firewall is not included with the free version ???
Opting out of any features is simple through a custom install.
. . . . and that option is cleverly scrolled off the bottom of the screen!
This is obviously a new tactic to try to get more users buying the full version by default. I must say I take a dim view of this sort of arm-twisting so if this happens again at the next re-registration I’ll probably dump Avast and go for MSE.