Explanation
These three objects are associated to the work type, as they define the skills, products, and service appointments that are related to the type of work performed. References:
https://help.salesforce.com/s/articleView?id=sf.fs_work_types.htm&type=5

To provide access to the Salesforce Field Service Mobile App, the user's profile must have the Field Service Mobile permission enabled.Updating Public Group membership, assigning a Field Service Mobile License to the user, or modifying the user record would not grant access to the mobile app. References:https://help.
salesforce.com/s/articleView?id=sf.fs_mobile_app_permissions.htm&type=5

Global optimization is a process that reschedules all service appointments within a specified time frame based on predefined criteria such as travel time or priority[82]. Global optimization doesn't reschedule appointments that have rule violations becauseit assumes that those appointments are manually scheduled by dispatchers for valid reasons[83]. There are no service resources available with the required skill levels because updating the skills required on the most common work types has increased the complexity of jobs and reduced the pool of qualified resources[84]. The optimizer uses a scheduling policy different from what is used on the dispatch console would not explain why the jobs are still scheduled to resources that lack the appropriate skill level.
Scheduling policies are records that define the optimization criteria for scheduling service appointments such as minimizing travel time or maximizing resource utilization[85]. The territory of the resources was not included in the global optimizationrequest would not explain why the jobs are still scheduled to resources that lack the appropriate skill level. Global optimization requests are records that specify which service territories and time frames should be optimized[86]. References: https://help.salesforce.com/s/articleView?id=sf.
fs_global_optimization_overview.htm&type=5 https://help.salesforce.com/s/articleView?id=sf.
fs_global_optimization_faq.htm&type=5 https://help.salesforce.com/s/articleView?id=sf.fs_skills_overview.
htm&type=5 https://help.salesforce.com/s/articleView?id=sf.fs_scheduling_policies_overview.
htm&type=5https://help.salesforce.com/s/articleView?id=sf.fs_global_optimization_requests_overview.
htm&type=5