I hope others experts comments and my addition will find you helpful to understand the concept. Learn how sap posting keys control debit and credit entries in financial accounting. As per sap best practices most of the transaction have already identified their combination posting keys so better we should use those.
In cloud , the posting key config is not open for change, and when you use different app to process business, the different posting keys will automatically be used at the backend ,which makes end users easily to handle daily operations. This document contains a list of posting keys used for accounting transactions, including the account type (asset, liability, expense, etc.), debit/credit indicator, and description for each key. To find the table of posting key, select any posting key at ob41, then press f1, then click on hammer icon the table used will be displayed.
First of all these are not posting keys, these are called as transaction keys and to get the complete list of standard list of these transaction keys, go to following path; Do users have access to tweak posting key configuration in the cloud system? For posting key tbsl is the table used.