In Godot 4.5.1.stable, it worked pretty well but in 4.6.0.stable it does not work.
In log, Godot may not loading pck file properly due to difference of disable_path_overrides to Godot 4.5.1. (Please refer error log)
ERROR: --main-pack was specified on the command line, but this Godot binary was compiled without support for path overrides. Aborting.
To be able to use it, use the disable_path_overrides=no SCons option when compiling Godot.
When I call initialize api of Godot, I used command line with –main-pack and pck file path.