Explanation
Minimum password length and password complexity requirement are two settings that administrators can configure to increase the security of user passwords in Salesforce. They determine how long and how complex the passwords must be to meet the security standards. Password different than username and prevent common words are not valid settings in Salesforce, although they are good practices for creating strong passwords.
References: https://help.salesforce.com/s/articleView?id=sf.admin_password_policies.htm&type=5

Explanation
To assign agent capacity and skill set, the administrator should enable Omni-Channel, which is a feature that allows agents to work on multiple cases or chats at once based on their availability and expertise.
Omni-Channel can route work items to agents based on their predefined capacity and skills, ensuring that they are working on the right tasks at the right time. Knowledge Management, Escalation Rules, and Territory Management are not related to agent capacity and skill set. References:
https://help.salesforce.com/s/articleView?id=sf.omnichannel_overview.htm&type=5

Explanation
Component visibility allows you to restrict the visibility of a related list based on a permission set.
References:
https://help.salesforce.com/s/articleView?id=sf.dynamic_forms_component_visibility.htm&type=5

Explanation
One of the possible causes for being unable to add a new user in Salesforce is that the username is already in use by another organization. Usernames must be globally unique across all Salesforce orgs, so if another user has claimed that username before, it cannot be used again. To fix this issue, choose a different username that is not taken by anyone else. The username is not restricted to a domain specific to my domain unless specified by an administrator. The email address used for the username does not have to match a contact record. The email used for the username can be any valid email address. References:
https://help.salesforce.com/s/articleView?id=sf.admin_usermgmt_add.htm&type=5

Explanation
An external ID is a custom field that has the external ID attribute enabled, which means it can be used as an identifier when importing and updating records from an external system. It allows administrators to match records based on a unique ID value from another system instead of using Salesforce record IDs, which may not be available or consistent across systems. An auto-number field is a custom field that automatically assigns a unique numeric value to each record, but it cannot be used as an identifier when importing and updating records from an external system because it is generated by Salesforce and may not match with the external system's IDs. A rich text field is a custom field that allows users to enter formatted text, images, and links, but it cannot be used as an identifier when importing and updating records from an external system because it is not unique or consistent across systems. A record ID is an internal ID assigned by Salesforce to each record, but it cannot be used as an identifier when importing and updating records from an external system because it may not be available or consistent across systems. References:
https://help.salesforce.com/s/articleView?id=sf.custom_field_attributes.htm&type=5