What does "link: false" mean in my Brewfile?
The link:false in the Brewfile appears to skip linking the installed binary in /usr/local/Cellar/... into /usr/local/bin (and thus my user $PATH) during bulk installation with brew bundle install.
I am guessing since python@3.8 was installed both as a dependency for something else (and thus not linked?) and it was also installed manually, it somehow erroneously was being output in the Brewfile as link: false though it should not have been.
Getting brew bundle dump to stop outputting the link: false was accomplished by forcibly uninstalling and reinstalling:
$ brew uninstall --ignore-dependencies python@3.8
$ brew install python@3.8
$ brew bundle dump