If you search for “Microsoft edge open source” there will come out a lot of blog posts from five years ago praising a Microsoft Press release that announces that edge is open source .
But then, there’s no actual repository, the GitHub is empty, there’s only the MIT license and that’s it
So, they publish the source somewhere or it’s just marketing?
The best I can find is in edge://terms it’s right at the bottom
Parts of the source code can be found at https://thirdpartysource.microsoft.com but it doesn’t appear to contain everything but I could be wrong on that
You need to send a cheque or money order of $5 including the version of Edge to Microsoft and they will send you the source code for Edge