how to fix the bundle install, quote:

It seems that the latest version of XCode tools (12 Beta 3) installs a version of Clang (the C compiler used by default on MacOS) that throws an error on implicit functions used on the native extension code of Puma.

Running the following:

bundle config build.puma --with-cflags="-Wno-error=implicit-function-declaration"
bundle install

Fixed the issue

How to fix LibSSL when install mysql2 gem driver

Also, whenever upgrading MySQL, always always always run:

mysql_upgrade

See https://www.hivelocity.net/kb/using-mysql_upgrade-command/