Updated builds.

build/three.cjs

@@ -67072,7 +67072,12 @@ function WebGLPrograms( renderer, environments, extensions, capabilities, bindin
 			useFog: material.fog === true,
 			fogExp2: ( !! fog && fog.isFogExp2 ),
 
-			flatShading: ( material.flatShading === true && material.wireframe === false ),
+			flatShading: material.wireframe === false && (
+				material.flatShading === true ||
+				( geometry.attributes.normal === undefined && HAS_NORMALMAP === false &&
+					( material.isMeshLambertMaterial || material.isMeshPhongMaterial || material.isMeshStandardMaterial || material.isMeshPhysicalMaterial )
+				)
+			),
 
 			sizeAttenuation: material.sizeAttenuation === true,
 			logarithmicDepthBuffer: logarithmicDepthBuffer,

build/three.module.js

@@ -7547,7 +7547,12 @@ function WebGLPrograms( renderer, environments, extensions, capabilities, bindin
 			useFog: material.fog === true,
 			fogExp2: ( !! fog && fog.isFogExp2 ),
 
-			flatShading: ( material.flatShading === true && material.wireframe === false ),
+			flatShading: material.wireframe === false && (
+				material.flatShading === true ||
+				( geometry.attributes.normal === undefined && HAS_NORMALMAP === false &&
+					( material.isMeshLambertMaterial || material.isMeshPhongMaterial || material.isMeshStandardMaterial || material.isMeshPhysicalMaterial )
+				)
+			),
 
 			sizeAttenuation: material.sizeAttenuation === true,
 			logarithmicDepthBuffer: logarithmicDepthBuffer,