CLI
I recommend using asdf to install the AWS CLI (currently named awscli in asdf). The manual installation leaves various bits of code strewn about that I hope is better contained by package managers (Homebrew does not seem to have it).
Auto prompt environment
To begin with, ignore marketing pages talking about the "aws shell". This is a dead project. But, parts of it appear to be now baked in to the aws cli v2. In particular aws --cli-auto-prompt.
You can configure the cli to automatically enter into the auto prompt environment by editing the ~/.aws/config file
[default]
cli_auto_prompt = on
At this point you should be able to type aws then on pressing enter you will enter into the auto prompt environment.