Add section to upgrade guide

Author: adamreeve

docs/source/library-user-guide/upgrading/54.0.0.md

@@ -438,3 +438,21 @@ clusters (e.g., ZWJ emoji sequences). For ASCII and most common Unicode text,
 behavior is unchanged.
 
 [#17861]: https://github.com/apache/datafusion/pull/17861
+
+### Conversion from `FileDecryptionProperties` to `ConfigFileDecryptionProperties` is now fallible.
+
+Previously, `ConfigFileDecryptionProperties` implemented `From<&Arc<FileDecryptionProperties>>`,
+and if an error was encountered when retrieving the footer key without providing key metadata,
+the error would be ignored and an empty footer key set in the result.
+This could lead to obscure errors later.
+
+`ConfigFileDecryptionProperties` now instead implements `TryFrom<&Arc<FileDecryptionProperties>>`,
+and errors retrieving the footer key will be propagated up.
+
+Code that uses `ConfigFileDecryptionProperties::from(&Arc<FileDecryptionProperties>)`
+should be updated to use `try_from`,
+and calls to `FileDecryptionProperties::into` should be changed to `try_into`,
+with appropriate error handling added.
+
+See [#21602](https://github.com/apache/datafusion/issues/21602) and
+[PR #21603](https://github.com/apache/datafusion/pull/21603) for details.