Microsoft released a free trial version in 2006. It features two missions and a limited area (St. Maarten) for those who want to test the mechanics before buying.
Despite being older than the 2020 version, FSX remains popular because: Microsoft Flight Simulator X Download Free Game
Thousands of free aircraft and scenery mods exist. Microsoft released a free trial version in 2006
You may see websites offering the full game for free. Please be cautious: Microsoft Flight Simulator X Download Free Game