"Preparing game data" is a recurring technical issue in StarCraft II
If you are looking to prepare your own data, these official and community-driven tools are the standard: google-deepmind/pysc2: StarCraft II Learning Environment starcraft ii preparing game data
Inside, find the Battle.net folder and delete the Cache directory. "Preparing game data" is a recurring technical issue
If you are stuck on this screen or it appears every time you play, try these solutions from Blizzard Support and community experts: starcraft ii preparing game data