> How is this GDPR compliant?
It isn't, really, but the question whom to prosecute is complicated. Clubhouse gets the contact list data from you, the user. Usually, somewhere in the ToS, there is a little thing where you confirm to have the right to share all the data you share with Clubhouse. That means that first and foremost, you as a user are responsible.
If you are a non-commercial user using Clubhouse from your private phone, what you do with your private contacts isn't covered by GDPR, private stuff is an exception. However, as consumer, European legislation protects you from surprising and unusual terms, which this might be. Legislation might also protect all your contacts. However, this is a question that still needs to be litigated in court, and I don't remember any decisions around that problem (WhatsApp basically has the same constellation).
If you are a commercial user, because this is your work phone and your contacts are colleagues, business partners, customers, things are quite different. You are, as a data processor, responsible for how you pass on your contact list. You better make sure that you are allowed to do that (because you have a GDPR-compliant reason like legal obligation, contractual obligation with your customer, assent or legitimate interest) and that your contacts have been informed about what you are doing beforehand. Also, you then need a written contract with Clubhouse about the data being passed along, about how it will be used and protected, etc. Also, passing along the contacts to Clubhouse must be necessary for a predetermined, well-defined reason that can be considered more important than your contacts' right to privacy.
So as a private person, you might get away with using Clubhouse. As a company, employee, self-employed, state official, whatever, you are probably in hot water, because surely you didn't do all the required things. But for Clubhouse this might not be a problem, because as current case law stands (imho, iirc, ianal, ...) Clubhouse isn't the party that did something wrong there.