From the outside and in, it is pretty much that same (both G26 based). Main difference would be floor level - slightly higher on the inside and the iDrive 8 dashboard.
You can check Thomas review of the M440i GC. Besides on what was already highlighted, the i4 also differs from 4 GC on 1) standard rear air suspension 2) blue highligts on gear shifter +start button 3) blue ring on BMW logos on the outside 4) partial covered grill 5 ) slightly different grill design 6) blue accents on exterior trim on non M sport versions.
Not sure if this was already posted but here is Thomas on Autogefühl reviewing the M440i GC. It’s the ICE version of the i4 and apart from drivetrain, rear suspension and idrive dashboard it’s an identical car to the i4.
At 1:50 he makes two door closings and“it’s ok, not that bad”, which seems much better than the “really bad” from the i4 m50 review. This car shouldn’t be a pre-production car as the i4 and probability has better fit and finish.