As a business analyst whats the most efficient way to quickly gain functional knowledge when you join a new company

The strength of a business analyst is their domain knowledge and ability to understand business process, gather requirements from business users and perform analysis and preparing requirements artefacts (BRD, process flow, UAT Document). Most of this information is gathered by interacting with business users.  As a first step the business analyst like any other employee should familiarise themselves with the company way of working, introducing themselves and making connection with fellow team members and business users.the BA next needs to understand the business process of the systems and application he/she will be supporting. This would require speaking to the business users to understand the as-is process, going through existing BRD and process flow documents to understand as-is structure. Regular 1:1 with key business stakeholders does help. BA also needs to establish relationship with the IT team, after all its them who will be implementing the BRD BA documents. BA needs to understand the current IT system and overview of teh technologies the current issues/challenges the IT team faces. This will help manage expectation with business users for any new requirements.