Are spot bitcoin ETFs a 'custodian'?

Excuse me, could you please clarify something for me? I've been hearing a lot about spot Bitcoin ETFs recently, and I'm wondering if they could be considered as a form of 'custodian' for bitcoin investors? I understand that ETFs track the performance of an asset or index, but does the term 'custodian' accurately describe their role in holding and managing bitcoin on behalf of investors? Or is there another term that better captures their function in the cryptocurrency market? Thank you in advance for your insights.