Most churches I’ve attended expect you to place membership with them.
There is absolutely no biblical requirement for this.
If you believe and are baptized by immersion in water in the name of Jesus or in the name of the Father, Son, and Holy Ghost you have become a member of the family. You are a member of the Church of Jesus Christ.
What you do with that membership is now up to you. Will you learn, follow, and grow in Christ or will you let your membership lapse?