I am posting the solution I performed for starting mysql as well as apache, php on macOS Catalina.
First, I have gone through the steps which I have shared earlier for Mojave.
Apache not working after macOS Mojave update
As I am using PHP 5.6 so I needed libphp5.so to make PHP 5.6 work after macOS upgrade. As before installing catalina, apache/php/mysql was working fine so I have the library already alavailable. I found the .so file using below command and updated the same in "/etc/apache2/httpd.conf"
sudo find / -name libphp5.so
after finding the file, I updated the same with path in /etc/apache2/httpd.conf
LoadModule php5_module
/usr/local/Cellar/php@5.6/5.6.25_1/libexec/apache2/libphp5.so
This makes the PHP 5.6 working but still mysql was failing with below error.
"[ERROR] Fatal error: Please read "Security" section of the manual to find out how to run mysqld as root!"
As it is my development area only so I simply did following:
1. goto the mysql installation bin directory
cd /usr/local/mysql-5.6.25-osx10.8-x86_64/bin
run the mysql with root as user.
sudo ./mysqld --user=root
it started the mysql too.