Property is also read for ??= and other assign ops

src/Analyser/NodeScopeResolver.php

@@ -629,6 +629,10 @@ private function processStmtNode(
 				if (!$node instanceof Expr) {
 					return;
 				}
+				if ($node instanceof Expr\AssignOp) {
+					$customCallback($node->var, $scope);
+					return;
+				}
 				if ($node instanceof Node\Scalar\EncapsedStringPart) {
 					return;
 				}

tests/PHPStan/Rules/DeadCode/UnusedPrivatePropertyRuleTest.php

@@ -138,4 +138,11 @@ public function testTrait(): void
 		$this->analyse([__DIR__ . '/data/private-property-trait.php'], []);
 	}
 
+	public function testBug3636(): void
+	{
+		$this->alwaysWrittenTags = [];
+		$this->alwaysReadTags = [];
+		$this->analyse([__DIR__ . '/data/bug-3636.php'], []);
+	}
+
 }

tests/PHPStan/Rules/DeadCode/data/bug-3636.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace Bug3636;
+
+class Foo
+{
+
+	/** @var \DateTimeImmutable */
+	private $date;
+
+	public function getDate(): \DateTimeImmutable
+	{
+		return $this->date ??= new \DateTimeImmutable();
+	}
+
+}