Yeah sounds like a big nothingburger to me. If you just use gitlab for private projects with basic pushing and pulling without any fancy gitlab features, switching is a matter of minutes.

Now, if you've built your entire company setup around gitlab and use everything they offer, yeah switching is gonna be a lot harder and will require more preparation. However, it's not impossible in the slightest. Even a large corporation with hundreds of developers could make a switch within 2 weeks.