Signing in
Email and password, Google, and Apple all sign in to the same account when they resolve to the same address. The web app and the iOS app share one account, so a password you change on one is the password you use on the other.
Password resets and email verification links are sent by Cretask from noreply@cretask.com. Cretask sends from that one address and no other, which makes anything claiming to be us from somewhere else easy to spot.
Your workspaces
Settings, Workspaces lists the workspaces you belong to, the invitations waiting for you, and the option to leave one. Leaving is yours to do; removing somebody else is an admin action from Settings, Members.
If you are the owner of a workspace you want to leave, transfer it first. A workspace never has zero owners.
Deleting your account
Settings, Security deletes your account. It is deliberate rather than instant: you re-authenticate first, because an account deletion should never be something a borrowed laptop can do.
Work you created in a shared workspace does not vanish with you, which would leave the rest of the team with holes in their projects. Hand over or delete anything you do not want left behind before you go.