Dear Ely Christiane,
Good day! Thanks for choosing Microsoft Community.
Based on your description, may l know whether you can see your shared calendar in your calendar list or not.
If you can see it in your calendar list, right click on it>choose Delete Calendar. Then it will not display on your calendar.
If you haven't opened the shared calendar in your Outlook, you don't need to delete it.
Besides, if you mean don't want to be a member of this shared calendar anymore, may l know if you are the owner of this shared calendar. Only the owner who created this shared calendar can remove the member via Shared mailboxes - Microsoft 365 admin center as shown in the following image. (When owner created the shared mailbox, a shared calendar was created automatically, so we need to remove member via shared mailbox)
If you have any other questions, please feel free to ask and give us feedback. Thanks for your patience and understanding. Stay safe and healthy.
Sincerely,
Tammy |Microsoft Community Moderator.