Conditional Formatting based on a specific rule

Then maybe this is what you are looking for?

Highlight different in all other projects = 
IF (
    HASONEVALUE ( 'Table'[Part Number] ),

    VAR _FirstProject = MIN ( 'Table'[ProjectName] )

    RETURN

    IF (
        CALCULATE (
            COUNTROWS ( VALUES ( 'Table'[ProjectName] ) ),
            ALLEXCEPT ( 'Table', 'Table'[Part Number] )
        ) > 1,

        VAR _PhysicalPartNumbersCurrentProject = 
            CALCULATETABLE (
                VALUES ( 'Table'[Part Physical Number] ),
                'Table'[ProjectName] = _FirstProject,
                ALL ( 'Table'[Part Physical Number] )
            )

        VAR _PhysicalPartNumbersOtherProjects =
            CALCULATETABLE (
                VALUES ( 'Table'[Part Physical Number] ),
                'Table'[ProjectName] <> _FirstProject,
                ALL ( 'Table'[Part Physical Number] )
            )

        VAR _DifferentPartNumbers = EXCEPT ( _PhysicalPartNumbersOtherProjects, _PhysicalPartNumbersCurrentProject )

        VAR _CurrentProjectOnlyPartNumbers = EXCEPT ( _PhysicalPartNumbersCurrentProject, _PhysicalPartNumbersOtherProjects )
        
        RETURN

        IF (
            COUNTROWS ( _DifferentPartNumbers ) + COUNTROWS ( _CurrentProjectOnlyPartNumbers ) > 0,
            "orange"
        )
    )
)

Highlight different physical part numbers in other projects

Your download link doesn't work anymore, but according to your data model, this should work:

Highlight different in all other projects = 
CALCULATE(
    IF (
        HASONEVALUE ( 'Parts'[Part Number] ),

        VAR _FirstProject = MIN ( 'Parts'[ProjectName] )

        RETURN

        IF (
            CALCULATE (
                COUNTROWS ( VALUES ( 'Parts'[ProjectName] ) ),
                ALLEXCEPT ( 'Parts', 'Parts'[Part Number] )
            ) > 1,

            VAR _PhysicalPartNumbersCurrentProject = 
                CALCULATETABLE (
                    VALUES ( 'Parts'[Part Physical Number] ),
                    'Parts'[ProjectName] = _FirstProject,
                    ALL ( 'Parts'[Part Physical Number] )
                )

            VAR _PhysicalPartNumbersOtherProjects =
                CALCULATETABLE (
                    VALUES ( 'Parts'[Part Physical Number] ),
                    'Parts'[ProjectName] <> _FirstProject,
                    ALL ( 'Parts'[Part Physical Number] )
                )

            VAR _DifferentPartNumbers = EXCEPT ( _PhysicalPartNumbersOtherProjects, _PhysicalPartNumbersCurrentProject )

            VAR _CurrentProjectOnlyPartNumbers = EXCEPT ( _PhysicalPartNumbersCurrentProject, _PhysicalPartNumbersOtherProjects )
            
            RETURN

            IF (
                COUNTROWS ( _DifferentPartNumbers ) + COUNTROWS ( _CurrentProjectOnlyPartNumbers ) > 0,
                "orange"
            )
        )
    ),
    ALL ( 'slicers'[project_code] ),
    ALL ( 'pj_code'[project_code] )
)

I'd love to see your Power BI guidelines 😉