An "option file" (OF) for Pro Evolution Soccer (PES) 2021 on PC is a user-created file package that restores or updates in-game team names, kits, logos, player names, competitions, and other assets that are not officially licensed in PES. Version 1.01.00 indicates a specific release iteration of such a file, typically adding fixes, new kits, updated transfers, and compatibility adjustments for the PC build.
Since PES 2021 is no longer officially updated by Konami, Option Files are the way to get: option file pes 2021 pc version 10100