br: fix description about case-sensitive and insensitive (#20438)

Author: RidRisR

br/backup-and-restore-overview.md

@@ -145,26 +145,25 @@ This section introduces the BR compatibility information for all [Long-Term Supp
 
 > **Note:**
 >
-> Known issue: Starting from version v7.2.0, fields of some system tables in newly created clusters become case-sensitive. However, for clusters that are **upgraded online** from versions earlier than v7.2.0 to v7.2.0 or later, the corresponding fields remain case-insensitive. Backup and restore operations involving system tables between these two types of clusters will fail. For more details, see [Issue #43717](https://github.com/pingcap/tidb/issues/43717).
+> Known issue: Starting from version v7.2.0, some system table fields in newly created clusters are case-insensitive. However, for clusters that are **upgraded online** from versions earlier than v7.2.0 to v7.2.0 or later, the corresponding system table fields remain case-sensitive. Backup and restore operations involving system tables between these two types of clusters might fail. For more details, see [Issue #43717](https://github.com/pingcap/tidb/issues/43717).
 
-The following table lists the compatibility matrix for full backups. For clusters upgraded from a version prior to v7.2.0 to v7.2.0 or later, their behavior is consistent with that of backups from v7.1.0.
+The following table lists the compatibility matrix for full backups. Note that all information in the table applies to newly created clusters. For clusters upgraded from a version earlier than v7.2.0 to v7.2.0 or later, their behavior is consistent with that of backups from v7.1.0.
 
 | Backup version | Compatible restore versions | Incompatible restore versions |
-|:---------|:----------------|:------------------|
-| v6.5.0    | 7.1.0           | v7.5.0 and later   |
-| v7.1.0    | -                 | v7.5.0 and later  |
-| v7.5.0    | v7.5.0 and later | -                 |
-| v8.1.0    | v8.1.0 and later | -                 |
+|:--|:--|:--|
+| v6.5.0 | 7.1.0 | v7.5.0 and later |
+| v7.1.0 | - | v7.5.0 and later |
+| v7.5.0 | v7.5.0 and later | - |
+| v8.1.0 | v8.1.0 and later | - |
 
-The following table lists the compatibility matrix for log backups. For clusters upgraded from a version prior to v7.2.0 to v7.2.0 or later, their behavior is consistent with that of backups from v7.1.0.
+The following table lists the compatibility matrix for log backups. Note that all information in the table applies to newly created clusters. For clusters upgraded from a version earlier than v7.2.0 to v7.2.0 or later, their behavior is consistent with that of backups from v7.1.0.
 
 | Backup version | Compatible restore versions | Incompatible restore versions |
-|:---------|:----------------|:------------------|
-| v6.5.0    | v7.1.0        | v7.5.0 and later  |
-| v7.1.0    | -                | v7.5.0 and later |
-| v7.5.0    | v7.5.0 and later | -                 |
-| v8.1.0    | v8.1.0 and later | -                 |
-
+|:--|:--|:--|
+| v6.5.0 | 7.1.0 | v7.5.0 and later |
+| v7.1.0 | - | v7.5.0 and later |
+| v7.5.0 | v7.5.0 and later | - |
+| v8.1.0 | v8.1.0 and later | - |
 > **Note:**
 >
 > - When only user data is backed up (full backup or log backup), all versions are compatible with each other.