My work here is done.
Typically when you install Windows 10 on a device
OR
When you step through the OOBE in the case of a new device purchase.....
Early on in the process you are prompted for a user name and password
THIS
Is generally a Microsoft Account, unless you purposely forgo that process and choose specifically to create a LOCAL account.
In the case of a local account I believe you can choose to leave the password blank (empty).
I do not believe that in the case of a Microsoft Account that, that is an option.
SUBSEQUENTLY
You have an option to add a PIN
ADDITIONALLY
You also have an option to add a Picture password
AND
You also have an option (assuming device support) you can opt for "Windows Hello"
I believe that in most if not all of the above scenarios there is an underlying user account with an accompanying password.
What that password might be and how you might recover or determine what it might be would depend on what steps you took in setting up the device initially