unbrew | Brew Cleanup Utility | Command Line Interface library

I will answer my own question for others who might run into a similar issue

After having uninstalled and reinstalled every single keg of brew I found the following solution:

1. Uninstall PHP
2. Run brew cleanup
3. Check your /usr/local/opt folder for any folders named php
4. Delete the folder (in my case it was called 'php@7.1')
5. Open a new terminal window
6. Run 'brew search php' in the terminal and make sure no php keg is installed.
7. Simply type 'php -v' in the terminal. For me this showed a version number, indicating that php was (at one point) installed without brew. You can choose to uninstall this version or update it to the newest version.

Conclusion

In my case I believe it was simply that PHP 7.1 was already installed and I installed a 2nd version (7.4) via brew.

The error 'Referenced from: /usr/local/opt/php@7.1/bin/php' was obviously searching for something in this folder and after deleted it, the error stopped.

First check where your node is installed by doing

I am using MacOS 10.6.8 (an old version of MacOS!). I installed, using nvm version 0.33.0, Node 10.15.3 and 8.16.0 and both of them gave me the error message about the dyld library shown in Ryuzaki's question above.

After some research I concluded that the libc++.1.dylib is not provided by the version of MacOS that I am using (it only came in on later versions of the OS). Therefore I loaded some earlier releases of Node, namely 6.17.1 and 4.9.1. Neither of these versions had the problem, leaving me to believe that the age of the OS is the problem.

The gpg-agent formula was removed by commit 965e1. The reason is given in the commit message:

The solution is probably simply to remove /usr/local/opt/python2/libexec/bin from your PATH environment variable.

To do this you have to edit your ~/.bash_profile and remove the occurence of this directory.

For anyone looking how to solve this issue, you have to delete the php and related libraries and install again as homebrew/php tap became deprecated and all of the libraries used to install became part of homebrew/core.

so by default you will php7.2 installed when you do $ brew isntall php but you can you install specific version manually like php@7.0. if you need xdebug you can install with pecl install xdebug and add the path in your php.ini

Yes, there’s a way to fix: delete them.

However, as brew doctor says:

Please note that these warnings are just used to help the Homebrew maintainers with debugging if you file an issue. If everything you use Homebrew for is working fine: please don't worry or file an issue; just ignore this. Thanks!

In other words: you don’t need to address any of the warnings from brew doctor if you don’t have any issue with Homebrew.

(Posted on behalf of the OP).

This is solved.

I followed this to show hidden files in my $PATH and establish a new $PATH. https://coolestguidesontheplanet.com/add-shell-path-osx/

Then un-installed and reinstalled pygame, following the comments here: https://www.reddit.com/r/Python/comments/2jfj1w/how_to_install_pygame_on_osx_1095/. Specifically the comment by redditor PigBoyOhBoy (with some adjustments for Python 2.7 rather than Python 3).

The easiest method I've found to fix this is to simply set the ownership of the folder to your username: