Install via Homebrew

brew install bash

See the Homebrew page for bash for the Bash version that the above command will installl. At the time of writing, this is 5.3.9:

Make new bash version your default

Run the below command to see the path for the bash binary just installed via Homebrew:

which bash

Add that to the end of /etc/shells.

For me, which bash returns:

/opt/homebrew/bin/bash

So I add that to the end of /etc/shells: