Happy New Year :
:
I’m pretty sure that friendsofphp/php-cs-fixer is a Magento dependency as I’ve found the same entry in my composer.json file in both my 2.2.x and 2.3.x installations. It’s used to automatically fix PHP Coding Standards issues.
The latest stable version is 2.16.1 released back in November. So, you might want to try updating that, as your version of 2.13.3 was released back in April. Once that blocker is out the way then you should be good to go.
Normally when a “blocker” appears like this, it’s because a “lock” has been put on the version. Something that I briefly touched on in this post entry: Error: "Unable to unserialize value" during composer update - #8 by digitalstartup.
I suspect your version of friendsofphp/php-cs-fixer is locked to the 2.13.x branch. Therefore, you might have to specify the version number when you run the composer require command for it.
Side Note: I wrote this reply before reading your other post… You got to the same conclusion
