Good communication is necessary, butI would put mutual interests way down on the list.
It’s good to have some so you can enjoy doing some of them together, but I think it’s very healthy to have some that are not. I think each person should have some interests that get them out with their friends. It keeps them well rounded and from getting too ingrown and dependent on each other.
I don’t know how to explain it, but I think maybe it keeps a person more well rounded.
Communication is important, but how and how well you communicate is something that changes with time.
My premise is that things that change over time are not "foundational".