Quick answer: Godot 4 exported PCK loaded successfully but ResourceLoader fails to find assets? Asset paths case-sensitivity mismatch between editor (Windows) and PCK (Linux) - normalize paths.
Editor on Windows works; PCK on Linux exports with case-mangled paths.
Lowercase all asset paths
Use lowercase folder and file names. Case-sensitive PCK + case-insensitive editor = mismatch.
Or normalize at load time
Custom ResourceFormatLoader normalizes case before looking up. Works for legacy projects.
Validate with godotpcktool
List PCK contents; cross-check against expected paths. Discrepancies surface upfront.
“Path case is a filesystem rule. Cross-platform projects need case-discipline.”
Establish lowercase paths as a convention. Document; enforce via lint. The bug class disappears.