Builder Patter and LSP

I was going through Builder pattern and had a couple of question that I thought needed clarification

1. Is builder pattern implemented through Abstract class or through interfaces. There are few posts that uses interface https://sourcemaking.com/design_patterns/builder
   https://refactoring.guru/design-patterns/builder
   ...can list more
   and others uses abstract class https://www.dofactory.com/net/builder-design-pattern

Note: The way I think is that it should be implemented using Abstract class. This rationale is based on the assumption that this way I may/may not implement them in derived class (as there could be a possibility that a few concrete class does not implement them)...
This assumption could be entirely wrong though.

2. If the above assumption is wrong then wont it violate LSP. Since one condition in LSP say that you cant have "not implemented methods" in your derived class.

Or I have misunderstood it completely...