Posting here to see if anyone has found a workaround and/or to get Apple employees' eyes on it.
I'm not sure when this bug was introduced but I've found that in Safari on iOS 27, I'm unable to download API keys from App Store Connect. Reported as a Safari bug in Feedback Assistant (FB24994724).
I checked web inspector's console and network logs for both my iPad and iPhone; no JS errors and a nondescript network error for the key's fetch request. Google Chrome for iPad/iPhone downloads the .p8 key file without issue, so this feels more like a Safari bug than an App Store Connect bug.