The official speedrunning leaderboards (on Speedrun.com) typically accept the Steam version only. However, many grassroots tournaments and "moderates" use v2579 Fitgirl because:
This article unpacks everything you need to know about this specific repack, the game’s cultural impact, and whether the Fitgirl version is the right path up the mountain. getting over it with bennett foddy v2579 fitgirl repack
The "v2579" tag refers to a specific build or update of the game. While not as widely publicized as major version launches (like 1.0 or the “Bennett’s Odyssey” updates), version 2579 typically includes: The official speedrunning leaderboards (on Speedrun