https://github.com/trending
Checkout plethora of topics such as "awesome <put your favorite domain>" repos for general exploration on any topic!
https://github.com/topics/awesome
There's also reverse interview question repo that I personally like.
https://github.com/viraptor/reverse-interview
Github also offers community curated collections of repos, for example there's one on chrome extensions to super charge your github experience: https://github.com/collections/github-browser-extensions
You'd be surprised to see what all you'll end up exploring!
PS: after writing this, I felt as if I am promoting github, but hey gitlab will always hold a special place for me.