Update: Turns out it works for others, apparently, and I also found one of my Macs where it does work, too. So it must be something pertinent to my systems. Oddly, though, the same ones where it now fails used to work because I had TestFlight enabled there before.
I have TestFlight set up on App Store Connect, and I have already about 50 testers subscribed.
Today, I found that the Public Link does not work any more:
Once TestFlight.app is installed, and one clicks the link to add my app to TestFlight, it always shows the error ""Unable to Open Link" in TestFlight.app:
I've tried this on several Macs (Ventura and Sonoma), and with different Accounts, both where the app was already added or not.
Is something generally broken, i.e. do others see the same issue with their TestFlight links, or is it just me? How do you suggest I get this resolved?
Here's an example link I set up for this purpose - it only allows a handful of subscribers, so please do not actually subscribe but just see if you even get allowed to, or if you get the same error if you must try: https://testflight.apple.com/join/oV8NNojg
And here's how it's set up: