diff --git a/CHANGELOG.md b/CHANGELOG.md
index 43e5ec716dd..936c7873a96 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,11 @@
 # Release Notes for Craft CMS 5
 
+## 5.1.6 - 2024-05-23
+
+- Added `craft\services\Fields::getRelationalFieldTypes()`.
+- Fixed a bug where `craft\helpers\Typecast::properties()` wasn’t typecasting numeric strings to ints for `int|string|null` properties. ([#14618](https://github.com/craftcms/cms/issues/14618))
+- Fixed a bug where “Related To” conditions weren’t allowing entries to be selected. ([#15058](https://github.com/craftcms/cms/issues/15058))
+
 ## 5.1.5 - 2024-05-22
 
 - Scalar element queries now set `$select` to the scalar expression, and `$orderBy`, `$limit`, and `$offset` to `null`, on the element query. ([#15001](https://github.com/craftcms/cms/issues/15001))
diff --git a/src/config/app.php b/src/config/app.php
index e182cba8263..8c2c895da1e 100644
--- a/src/config/app.php
+++ b/src/config/app.php
@@ -3,7 +3,7 @@
 return [
     'id' => 'CraftCMS',
     'name' => 'Craft CMS',
-    'version' => '5.1.5',
+    'version' => '5.1.6',
     'schemaVersion' => '5.0.0.20',
     'minVersionRequired' => '4.4.0',
     'basePath' => dirname(__DIR__), // Defines the @app alias
diff --git a/src/elements/conditions/RelatedToConditionRule.php b/src/elements/conditions/RelatedToConditionRule.php
index 794b9ca7864..38eea615172 100644
--- a/src/elements/conditions/RelatedToConditionRule.php
+++ b/src/elements/conditions/RelatedToConditionRule.php
@@ -5,9 +5,9 @@
 use Craft;
 use craft\base\conditions\BaseElementSelectConditionRule;
 use craft\base\ElementInterface;
-use craft\base\NestedElementInterface;
 use craft\elements\db\ElementQueryInterface;
 use craft\elements\Entry;
+use craft\fields\BaseRelationField;
 use craft\helpers\Cp;
 use craft\helpers\Html;
 use craft\helpers\UrlHelper;
@@ -94,15 +94,14 @@ protected function inputHtml(): string
     private function _elementTypeOptions(): array
     {
         $options = [];
-        foreach (Craft::$app->getElements()->getAllElementTypes() as $elementType) {
+        foreach (Craft::$app->getFields()->getRelationalFieldTypes() as $field) {
+            /** @var string|BaseRelationField $field */
             /** @var string|ElementInterface $elementType */
-            /** @phpstan-var class-string<ElementInterface>|ElementInterface $elementType */
-            if (!is_subclass_of($elementType, NestedElementInterface::class)) {
-                $options[] = [
-                    'value' => $elementType,
-                    'label' => $elementType::displayName(),
-                ];
-            }
+            $elementType = $field::elementType();
+            $options[] = [
+                'value' => $elementType,
+                'label' => $elementType::displayName(),
+            ];
         }
         return $options;
     }
diff --git a/src/helpers/Typecast.php b/src/helpers/Typecast.php
index 2e12f7aab72..fb031da2195 100644
--- a/src/helpers/Typecast.php
+++ b/src/helpers/Typecast.php
@@ -169,7 +169,7 @@ private static function _propertyType(string $class, string $property): array|fa
                 return [self::TYPE_INT_FLOAT, in_array(self::TYPE_NULL, $names)];
             }
             // Special case for int|string
-            if ($names === [self::TYPE_INT, self::TYPE_STRING] || $names === [self::TYPE_INT, self::TYPE_STRING, self::TYPE_NULL]) {
+            if ($names === [self::TYPE_INT, self::TYPE_STRING] || $names === [self::TYPE_INT, self::TYPE_NULL, self::TYPE_STRING]) {
                 return [self::TYPE_INT_STRING, in_array(self::TYPE_NULL, $names)];
             }
         }
diff --git a/src/services/Fields.php b/src/services/Fields.php
index 6ba6a43693c..075e5525743 100644
--- a/src/services/Fields.php
+++ b/src/services/Fields.php
@@ -27,6 +27,7 @@
 use craft\fieldlayoutelements\CustomField;
 use craft\fields\Addresses as AddressesField;
 use craft\fields\Assets as AssetsField;
+use craft\fields\BaseRelationField;
 use craft\fields\Categories as CategoriesField;
 use craft\fields\Checkboxes;
 use craft\fields\Color;
@@ -334,6 +335,25 @@ public function getNestedEntryFieldTypes(): array
         return $fieldTypes;
     }
 
+    /**
+     * Returns all available relational field type classes.
+     *
+     * @return string[] The available relational field type classes
+     * @phpstan-return class-string<BaseRelationField>[]
+     * @since 5.1.6
+     */
+    public function getRelationalFieldTypes(): array
+    {
+        $relationalFields = [];
+        foreach ($this->getAllFieldTypes() as $fieldClass) {
+            if (is_subclass_of($fieldClass, BaseRelationField::class)) {
+                $relationalFields[] = $fieldClass;
+            }
+        }
+
+        return $relationalFields;
+    }
+
     /**
      * Creates a field with a given config.
      *