Hello there Tjb1965,
I see you're having a problem with your iCloud emails missing, so let's look into this.
As you stated that the inbox appears to be empty, let's get started by checking your available iCloud storage. You'll want to be sure that you have available storage, and you can also check to see what the reported storage for your email would be to see if there should be information shown. For help with this, take a look at the following resource:
Manage your iCloud storage
If you see that your storage is full, you can upgrade the iCloud storage using the steps here:
Upgrade to iCloud+
If you see that this isn't related to your iCloud storage, let's look through the following steps once more to see if this will clear up what is occurring.
If iCloud Mail isn't working
If you still see that you're unable to generate your emails, try logging into your account online to see if you're able to view your emails at iCloud.com.
We hope this is able to help, but if not then you'll want to Contact Apple Support so this can be looked into in more detail.
Cheers!