Does the presence of a .ssh directory force remote access via Public key authentication?

Context: 24.04 Ubuntu on Raspberry Pi The default user is ubuntu. For this discussion let's define different scenarios: 1) the directory /home/ubuntu/.ssh does not exist 2) an empty directory exists as: /home/ubuntu/.ssh 3) a file exists as /home/ubuntu/.ssh/authorized_keys Q1) Which, if any, scenarios force remote access password authentication require public key authentication? Q2) Is it enough to copy my public key (id_rsa.pub) from a MacBook, via USB memory stick, to the rPi: /home/ubuntu/.ssh/authorized_keys? or there some other item / setting that needs to be configured to enable remote ssh access (either password or public key)? Q3) What forces remote access via Public Key Authentication and exclude password authentication? The default user (ubuntu) has a passord, which enables terminal access via rPi's keyboard Q4) Is it possible to configure the default user (ubuntu) for remote ssh access via public key? or is it necessary to create a new user.