Even with users asking, it's not a good idea to put a beta of your app out until it's ready. Max points out that even though they could put a beta out of Ulysses for iOS 13, it's still too buggy.
Releasing a post like this and explaining why there's no beta available is a great move. You can always point any user to this post to stay updated. You could also have a signup form for beta testers on the page if you wanted.
Most impactful for us, however, is that the (great, great) updates done to iCloud are also leading to severe problems with the service.
A Word About Apple’s OS Betas by Max Seelemann