laravel main error undefined variable in mail componet code example

Example: Undefined variable: subcopy laravel mail

This issue usually arises after a Laravel upgrade,as laravel update the view 
files and vendor files. So it's about making sure that all blade templates are 
up to date. 

And for this issue inside your resources/views/vendor/mail/html/layout.php
for this issue updating `or` to `??` will resolve you issue.