Explanation
Box 1: IsOptimisticConcurrencyEnabled
On a multi-threaded and multi-user system like Power Apps, operations and data changes often happen in parallel. A problem arises when two or more update or delete operations on the same piece of data happen at the same time. This situation could potentially result in data loss. The optimistic concurrency feature provides the ability for your applications to detect whether a table record has changed on the server in the time between when your application retrieved the record and when it tries to update or delete that record.
Box 2: If-Match: Etag
Use If-Match and If-None-Match headers with ETag values to check whether the current version of a resource matches the one last retrieved, matches any previous version or matches no version. These comparisons form the basis of conditional operation support. Dataverse provides ETags to support conditional retrievals, optimistic concurrency, and limited upsert operations.
Reference:
https://docs.microsoft.com/en-us/powerapps/developer/data-platform/optimistic-concurrency
https://docs.microsoft.com/en-us/powerapps/developer/data-platform/webapi/perform-conditional-operations-usi
https://docs.microsoft.com/en-us/powerapps/developer/data-platform/webapi/perform-conditional-operations-usi