Elasticsearch 6.3.2 rolling upgrade to 6.8.22, should the application elasticsearch-rest-high-level-client be upgraded to 6.8.22

Refer to an official article:

The 6.0 client is able to communicate with any 6.x Elasticsearch node, while the 6.1 client is for sure able to communicate with 6.1, 6.2 and any later 6.x version, but there may be incompatibility issues when communicating with a previous Elasticsearch node version, for instance between 6.1 and 6.0, in case the 6.1 client supports new request body fields for some APIs that are not known by the 6.0 node(s).

So can it be considered that Java High Level REST Client
6.3.2 Can access communication with Elasticsearch 6.8.22?

Yes. But you won't have access to any of the newer features of Elasticsearch until you upgrade the client.