For S/4 HANA OnPremise, we have the following FAQs:

2578294 - FAQ - Employee to Business Partner synchronization in S/4HANA OnPremise
2409229 - Employee Synchronization Report: FAQ

and for S/4 HANA CLOUD:

2555311 - FAQ - Import Employees app

and for SF integrated with S/4 HANA CLOUD:

2882329 - Common issues during the SF -> S/4HC replication

and for the usage of the API Replicate Basic Master Data for Workforce from External HR Systems

2905918 - FAQ: Replicate Basic Master Data for Workforce from External HR Systems