If you have runtime configuration to allow unsupported features, please be aware that the keys to allow use of runtime features changed with
https://github.com/envoyproxy/envoy/pull/9591
The old way to allow fatal-by-defaults was
envoy.deprecated_features:proto_file.proto:field_name
the new way is
envoy.deprecated_features:full.namespace.field_name
If you're updating your configs to the latest and greatest as you go, you can just ignore this and carry on :-)
cheers,
Alyssa