This question is for Protestants who don’t believe in the institutional Church. If you accept the Nicene Creed, what do you mean when you say you believe in the one, holy, catholic and apostolic church? If the church is nothing more than the body of all believers, what does it mean to believe in the body of all believers? It strikes me as about like saying I believe in the body of all left-handed people.
Many Protestant denominations don’t recite the Nicene Creed. The Church of England does, with catholic in very definite lower case.
The unity is the unity of belief, nothing more, nothing less.