I have a similar issue with the 0.4 demo build on Linux: The game crashes when I try to open the build menu, but with a different error:
ERROR: get_as_text: Condition "!f" is true. Returned: String()
At: core/bind/core_bind.cpp:2106.
ERROR: call: Error parsing JSON at line 0:
At: modules/gdscript/gdscript_functions.cpp:1268.
WARNING: set_enabled_focus_mode: BaseButton's Enabled Focus Mode property has been deprecated due to redundancy and will be removed in Godot 4.0. Please use Control.set_focus_mode instead.
At: scene/gui/base_button.cpp:329.