Explanation
The User Licenses related list in Company Information shows the types of licenses that have been purchased for an org and how many are available or used. It also shows the expiration date of each license type if applicable. This information can help administrators plan for license purchases and manage user access.
Searching for license types in setup does not show how many licenses have been purchased or how many are available or used. User Management settings in setup does not show license information either, but rather settings related to user login, session, identity, etc. Usage-based entitlement related list in company information shows information about usage-based licenses such as API requests or sandboxes, but not user licenses. References:
https://help.salesforce.com/s/articleView?id=sf.users_understanding_license_types.htm&type=5

Explanation
Report folders are used to organize and secure reports in Salesforce. You can set different levels of access for different users or groups on each report folder. To preserve the integrity of the source reports for dashboards, you can create a new report folder with viewer access only and move the dashboard reports to that folder. This way, users can view the reports but not edit them. References:
https://help.salesforce.com/s/articleView?id=sf.reports_folders.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.reports_dashboard_folder_access.htm&type=5

Explanation
Big Deal Alerts are notifications that are sent to users when an opportunity reaches a certain amount, probability, or stage. They can be configured by administrators to alert sales reps or managers when they have a high likelihood of winning a big deal. Key Deals are a feature of Einstein Opportunity Scoring that shows the top opportunities based on their score and stage, but they do not send notifications. Activity Timeline is a component of Lightning Experience that shows the past and upcoming activities related to a record, but it does not notify users of big deals. Performance chart is a type of report chart that shows how well users or teams are performing against their goals, but it does not alert users of big deals. References:
https://help.salesforce.com/s/articleView?id=sf.forecasts3_big_deal.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
Page layout and field level security are two factors that determine whether a user can see a new field on a record. To troubleshoot this issue, the administrator should ensure that the page layout for the user's profile has been updated to include the new field and that the field level security of the field for the user profile allows read or edit access. References:
https://help.salesforce.com/s/articleView?id=sf.customize_layoutoverview.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.admin_fls.htm&type=5