Currently, there's no ability to customize the deserialization that happens behind the scenes when using JsonCommands.Get<T>() or JsonCommandsAsync.GetAsync<T>().
They both use the System.Text.Json's JsonSerializer Deserialize<TValue>(string, JsonSerializerOptions? options = default), which can accept a JsonSerializerOptions parameter to control how the deserialization is done. This means that users can not use the Redis json to command if they want case insensitive or any custom behavior (such as string-enum-converters).
I think it would be fairly simple to add an optional parameter to the JsonCommands to then use in its internal call to the JsonSerializer.
I'm happy to submit a PR if you'd like.