Lineage is not about providing a google free version of Android. It does not contain google apps, for licensing reasons, probably also to let the user choose. But it does not go further, all the other stuff like captive portal check, agps, dns etc still uses google servers. It’s not “degoogled” in any way. Love lineage btw but we need to be aware of what it is and isn’t.
Most brands allow relocking bootloader. But after that you with be only able to use stock rom. Pixel lets you lock the bootloader with a different signature, so in this example you are basically able to lock it to only boot grapheneos and nothing else.