@Heroi1200
This is a misconception. Once an .uasset is saved in a newer version of the engine (like 5.4) it can’t be opened in an older version. There is a “package version” check which for 5.4 is ~1012. If the package version is newer than the currently opened UE version, the asset won’t open. My Asset Downgrader | Fab is the only way to downgrade assets.