How do I block youtube.com on all browsers on my MacBook instead of only blocking it on Safari?

Besides editing the hosts file or changing your router settings, you could try using an app like AppCrypt to block youtube.com across all browsers on your Mac. It offers a free trial, so you can give it a try and see if it meets your needs.

The simplest way is to edit the hosts file to point the url to your local host which is 127.0.0.1, however as pointed out, there may be multiple urls that have to be blocked in this way.

There are a number of different ways to block access to specific websites, some work better than others and some are more technical than others. Watch this video from MacMost for an overview.

The problem is, there is almost always a way to work around the block. YouTube, for example, is accessible via multiple addresses; you would need to know & block every one.

Then there is the matter that you are only blocking on a single device (your MBPro) not all devices. If necessary you may want to investigate blocking the site(s) in your router rather than on the Mac or other devices (computers, phones, etc.)