They are very different.

GrapheneOS' whole thing is security and privacy. It's big on sandboxing apps and browser sessions. Google Play and most Android features are opt-in (Google Play Services are also sandboxed). Just check their features.

LineageOS doesn't have most of the above. It's mostly just a regular barebones Android distribution without all the vendor bloat, and a great alternative if you just want more control and less BS (if you've used a Samsung device you will know what I mean - absolutely horrible distribution imo).