add the unsupported note to require_secure_transport

system-variables.md

@@ -738,6 +738,11 @@ mysql> SHOW GLOBAL VARIABLES LIKE 'max_prepared_stmt_count';
 
 ### require_secure_transport <span class="version-mark">New in v6.1.0</span>
 
+> **Note:**
+>
+> This variable is not supported on [TiDB Dedicated](https://docs.pingcap.com/tidbcloud/select-cluster-tier#tidb-dedicated).
+> If you open it, it may cause the SQL client to fail to connect to the TiDB Dedicated cluster.
+
 - Scope: GLOBAL
 - Persists to cluster: Yes
 - Type: Boolean

tidb-cloud/limited-sql-features.md

@@ -134,6 +134,7 @@ TiDB Cloud works with almost all workloads that TiDB supports, but there are som
 | `max_allowed_packet` | No limitation | Read-only [^11] |
 | `plugin_dir` | No limitation | Not supported [^8] |
 | `plugin_load` | No limitation | Not supported [^8] |
+| `require_secure_transport` | Not supported [^13] | Read-only [^11] |
 | `skip_name_resolve` | No limitation | Read-only [^11] |
 | `sql_log_bin` | No limitation | Read-only [^11] |
 | `tidb_cdc_write_source` | No limitation | Read-only [^11] |
@@ -246,3 +247,5 @@ TiDB Cloud works with almost all workloads that TiDB supports, but there are som
 [^11]: The variable is read-only on TiDB Serverless.
 
 [^12]: Customizing cache size using [`AUTO_ID_CACHE`](/auto-increment.md#cache-size-control) is temporarily unavailable on TiDB Serverless.
+
+[^13]: Not supported. Enabling it for TiDB Dedicated clusters will result in SQL client connection failures.