I should have said that when I saw the "install the latest version..." message that I did install the latest version. Also, the AppGallery app runs perfectly.
I have just tried changing my app's manifest to target SDK 29 (it was 33) and my app works. So it would seem the Huawei FAQ I quoted is correct, in that the requirement to update the Huawei SDK starts with Android 11 (SDK30). Of course, I would like to be able to target my app at an SDK higher than 29.