WARNING: Module mcrypt ini file doesn't exist under /etc/php/7.2/mods-available

Pointing to php7.1-mcrypt with php7.2 will solve the issue here. Below are the steps to configure 7.1 version mcrypt with php7.2

Install php7.1-mcrypt

sudo apt install php7.1-mcrypt

Create symbolic link to php7.1-mcrypt

sudo ln -s /etc/php/7.1/mods-available/mcrypt.ini /etc/php/7.2/mods-available/

Enable mcrypt extension

sudo phpenmod mcrypt

Restart the FastCGI Process Manager service

sudo service php7.2-fpm restart

Note:
The above solution is a workaround to enable mcrypt in php7.2 through apt till php7.2-mcrypt is not available.

for php-7.3 like mentioned above i had to execute this command

sudo ln -s /etc/php/7.0/mods-available/mcrypt.ini /etc/php/7.3/mods-available/ cause the version 7.0 comes by default.