OP here, posting this as I am experiencing this issue with links from e.g. Google on Safari, and links from in-app webviews. I thought the MacRumours link shows the extent of the issue but happy for the link to be changed to a more reliable source if there is one - I couldn't find anything.

Shocked that such a huge bug could slip through making a major part of the phone useless! It actually makes me reconsider my loyalty to the iPhone as I thought stability was one of the key advantages of Apple's closed/limited device combination ecosystem, but if such a bug arose on Android, I'd at least be able to change the default browser.

Workaround seems to be to use Chrome for now but that doesn't help with in-app webviews.