How many user accounts should be found when I run "useraccount list all" when there is only 1 person using personal computer?
The amount of useraccounts on a windows pc is not tied to the amount of people using the pc.
Although each user is likely to have one user, it is possible for anyone to create a user. This can be a testuser, or a user with admin rights together with a user with standard rights.
If we speculate that there is just one user account called "User" which the enduser is using and has administrative rights, then one could expect between 3 and 6 users to be present.
There always will be an Administrator user which is required for UAC and elevation to work, despite if a user has administrator rights or not.
I've also seen a Guest user, even though this is disabled.
Then there is a DefaultAccount, also disabled, which is used to create a new user. This user is copied. The reason behind this default account, is so you can setup rights for new users.
Then there is the WDGAUtilityAccount, also disabled, which is used for Windows Defender.
If you install certain software, such as IIS, it may also create additional useraccounts that are disabled. Earlier versions of windows may create serviceaccounts. If you used Windows 7 and upgraded to Windows 10, it is likely that you will see these useraccounts come back. I forgot however what their usernames are, but it are usually 2 accounts.
As you can see, I can't give you an exact answer, because there are many factors that will determine how many and which users you will find.
Useraccount list all will in any case list all of them.
Is it bad if you see many accounts? No, but if you go to Computer management, Local users and groups, Users, you will find the same list of users, and a description for each user that is not an actual user, explaining what the user does. This should help you distinguish users that do not belong there vs users that should be there.
If you are still in doubt, then post a question and ask for that specific user, or google that username.
It is also possible that if your pc is managed by your organisation, that they create an admin user. In that case, you will find it here. The usage for an admin user is usually so access can be granted to a system where the user forgot their password and can no longer get in in any other way. The admin user could then be used to reset the password. Note, this is only common practice if the pc is not domain joined. A domain joined pc does not require the present of a second local administrator user.