Hi there,
I’ve gone through all of the steps shown here Unreal Engine 4 on GitHub - Unreal Engine
I’ve had an Unreal Account for years, just created a Github account, linked the two together and received a confirmation email.
While logged into my Github account, I attempt to access https://github.com/EpicGames/UnrealEngine but get a 404 error.
Also having trouble trying to access https://github.com/EpicGames/UnrealEngine through Github Desktop.
Any help is much appreciated!
SOLVED
Received a reply on answerhub from Fatorice
“Look into your GitHub account settings and check, if you can find EpicGames as a linked account. When yes, try to remove it and disconnect it of the EpicGames website also. Try to connect it again. You should get an invite link from github as well, if I remember this correctly. When this doesn’t work, try to create a new EpicGames and a new GitHub account. I had problems as well and this fixed it for me 
Hope this helps”
So I’m not sure if this was my fault or because I created a new Epic Games account, but after creating the new account and relinking it to Github, I went to this page again https://github.com/EpicGames/UnrealEngine and saw a notification at the top saying an Admin has asked me to join Epic Games (not verbatim). So I clicked Join and now I have access! It’s possible I missed this notification before or the notification wasn’t showing up previously.