It took a few weeks at odd hours, but I have finally deployed the latest version of Weather Now (5.0.8507). I didn't update anything visual, but all the plumbing got a refresh. It's now running in .NET 7 (until November, when .NET 8 comes out), and I did a top-to-bottom review of its asynchronous code.
The app now runs noticeably faster, and I believe the corrections to the async bits will cure the nagging (but invisible) problem of thread exhaustion that happened from time to time.
Now I can start making some other fixes and adding some long-missing features. Really, I just needed to get back into the swing of it.