I do not know if GitLab does anything different; I've never used it in anger. I'd bet $10 the answer is "no, it's basically just the same as GitHub", though.
If you want a service that adds stacking on top of GitHub, my conclusion after some research is that https://graphite.dev/ is the best option. We did consider it, but it couldn't work in my last job for "reasons" (see my other replies in this thread) but if you've got a shop of Git users and just want to throw money at the problem, I think it's the best choice.
GerritHub is also a possibility, they employ many of the Gerrit devs and know what they're doing, but holy shit the corporate options are expensive out of the gate. It's like $20k/yr minimum regardless of size or number of users.
Honestly, Graphite is cheap as hell considering how much more productive your engineers can be with a good review tool. Gerrit was basically night and day for us. It's not "oh, it pays for itself really quickly in a few days!" You'd probably pay off the monthly cost in less than an hour of actual code review. And you don't even have to opt most of your engineers in; you can trial it where 90% of them use GH and only a subset use graphite and pay.