Adjust

Author: Youssef1313

src/Microsoft.OpenApi/Models/OpenApiSchema.cs

@@ -1177,12 +1177,12 @@ private void SerializeNullable(IOpenApiWriter writer, OpenApiSpecVersion version
         private (JsonSchemaType Type, string Format)? GetKnownTypeAndFormatPreOpenApi31()
         {
             // https://spec.openapis.org/oas/v3.2.0.html#migrating-binary-descriptions-from-oas-3-0
-            if (Type is not null && Type.Value.HasFlag(JsonSchemaType.String) && ContentEncoding == "base64")
+            if (Type == JsonSchemaType.String && ContentEncoding == "base64" && !string.IsNullOrEmpty(ContentMediaType))
             {
-                return (Type.Value, "byte");
+                return (JsonSchemaType.String, "byte");
             }
 
-            if (Type is null && !string.IsNullOrEmpty(ContentMediaType))
+            if (Type is null && ContentEncoding is null && !string.IsNullOrEmpty(ContentMediaType))
             {
                 return (JsonSchemaType.String, "binary");
             }

test/Microsoft.OpenApi.Tests/Models/OpenApiSchemaTests.cs

@@ -1554,8 +1554,6 @@ public async Task SerializeMissingPropertiesEmitsOaiExtensionsInV3()
         {
             var expected = JsonNode.Parse("""
                 {
-                  "type": "string",
-                  "format": "binary",
                   "x-jsonschema-$anchor": "root",
                   "x-jsonschema-contentEncoding": "base64",
                   "x-jsonschema-contentMediaType": "application/jwt",