It seems you need to move the fixture under

https://github.com/rectorphp/rector-src/tree/main/rules-tests/TypeDeclaration/Rector/Property/TypedPropertyFromAssignsRector/FixtureComplexTypes

to demonstrate invalid usage on php8+ feature

Various notes:

• The php74 env for nullable change is correct, just to keep the docblock DateTime&MockObject
• Under php8+, the change is incorrect for combine nullable with intersection:

+    private ?\DateTime&\PHPUnit\Framework\MockObject\MockObject $property = null;

Ref https://getrector.org/demo/9639d6c3-b5a5-47ef-8565-f3037cde9e64

nullable can't be combined with intersection directly, see:

https://3v4l.org/QQi2E#v8.2.0 (nullable ?)
https://3v4l.org/QP7Rh#v8.2.0 (union nullable)

so it should be :

+    private null|(\DateTime&\PHPUnit\Framework\MockObject\MockObject) $property = null;

Based on above notes, it seems the solution is skip on php 7.4 and 8.0 for that, and apply changes on php 8.1+ with intersection types enabled:

-    /**
-     * @var DateTime&MockObject
-     */
+    private null|(\DateTime&\PHPUnit\Framework\MockObject\MockObject) $property = null;

like @VincentLanglet comment at rectorphp/rector#7692 (comment)

Actually, without the setUp() called, nullable still ok on php 7.4, but just not to remove the docblock

@puniserv I cherry-picked your commit at PR #3372