Theres no vendor lock-in if you can scp your codebase to any vps and run `next build && next start` and have it work out of the box
It is literally MIT licensed software. It’s no more vendor lock-in than React is in the first place.
the license wouldn't be that important if say it was just covering over a vercel specific API. that's not the case here, but the license would be irrelevant if it's just talking to a vendor locked service.