There's no real "right" algorithm, it always depends on what you're trying to do.
What you're describing sounds like clustering to me. You want to maybe identify "islands" of nodes in a bigger graph based on what is related to what, and if things are interrelated then you might say they're similar to one another.
Have a look here, in the community detection section: https://neo4j.com/docs/graph-data-science/current/algorithms/
There are many different ways to do this. I would start with some of those community detection algorithms, and then if you find they don't do the right thing for you, ask another question with more specifics about why they're not right and what additional you're looking for. Ultimately there is a big set of graph algorithms and they all do slightly different things, so it's a wide space to choose from, but to get a good algorithm recommendation you need to be specific about which outcome you want.
