Pacstall is the AUR Ubuntu wishes it had. It takes the concept of the AUR and puts a spin on it, making it easier to install programs without scouring github repos and the likes.
Pacstall has fully supported auto completions for the bash, and fish shells. For the ZSH shell you can emulate the completions using the following commands.
Zsh can emulate bash completion scripts by default so all you have to do is add these to your .zshrc or wherever you source things: