I was able to install Charles Proxy 3 (sudo apt install charles-proxy3) but unable to find the package for 4.
https://www.charlesproxy.com/documentation/installation/apt-repository/
Install GPG public key
wget -q -O - https://www.charlesproxy.com/packages/apt/PublicKey | sudo apt-key add -
Add repo to your sources -
sudo sh -c 'echo deb https://www.charlesproxy.com/packages/apt/ charles-proxy main > /etc/apt/sources.list.d/charles.list'
update sources and install charles
sudo apt-get update
sudo apt-get install charles-proxy
The package creates a "charles" command in /usr/bin, and adds Charles in your application menus in your window manager.
Verify -
athakur@athakur-Inspiron-7560:~$ charles -version
Charles Proxy 4.2.1