E: The repository 'http://ppa.launchpad.net/webupd8team/tor-browser/ubuntu bionic Release' does not have a Release file. W: Updating from such a repository can't be done securely, and is therefore disabled by default. W: See apt-secure(8) manpage for repository creation and user configuration details
The tor-browser package in that ppa has not been updated in a very long time, I do not recommend using it. My suggestion is to remove that ppa, to get AppCenter working again, and then install tor from the ubuntu repository (as per the Tor Project's instructions).
To remove the obsolete ppa:
sudo add-apt-repository --remove ppa:webupd8team/tor-browser
After that, run
sudo apt update to see if the error is gone. If all is well, try running
sudo apt upgrade to bring your system up-to-date.