I did, yes - or rather I put it behind a UA check. I've just put up a reproducible case behind a query-string flag - see edit above.

This does cause a crash on my iPhone XR running iOS 14.5

I confirm not crashing for me on MacOS Mojave with Safari 14.1:

https://streamable.com/5jn41o

That's interesting - so a Mobile Safari issue but not a desktop one. Cheers.

I confirm I can trigger the bug in iOS 14.5 on my iPhone 11. Interestingly, the first time I click on "From" or "To" I get a forced refresh.

It's crashing both times, it's just that the first time, Safari reloads the page. The second time, it gives you the "repeatedly" crashing message.

That's not surprising, I've seen a lot of cases where Mobile Safari has different bugs than the desktop one.

OP said the bug appeared on iOS 14.5

The main linked article is about Safari 14.1 on MacOS. If it is "exactly the same issue" as OP says, then how come it doesn't appear on Safari 14.1 on MacOS?

It's probably not a Safari bug.

Possibly. But then there's no way to confirm it happens on a lot of devices. So far I've been unable to reproduce the issue on any of my MacOS and iOS devices on any problem-related URL I was given in this thread or linked discussions.

Trello evidently had a bug (or rather, Safari 14.1 evidently has a bug which manifested on Trello) related to Intl.NumberFormat:

https://community.atlassian.com/t5/Trello-questions/Re-Trell...

Does the following work for you in Safari 14.1?

new Intl.NumberFormat('en-US', {notation: 'compact'}).format(1825602)

In Chrome this gives "1.8M"

I encounter the same issue which for me breaks Microsoft's documentation, e.g. https://docs.microsoft.com/en-us/dotnet/api/system.io.memory...

I get (macOS 10.14.6, Safari 14.1):

  > new Intl.NumberFormat('en-US', {notation: 'compact'}).format(1825602)
  < TypeError: Failed to initialize NumberFormat since used feature is not supported in the linked ICU version

Is that even the same issue?

It is the root cause of some issue with Trello that appeared with Safari 14.1, but perhaps not the same issue causing other sites to break; if so, perhaps there are multiple bugs with the update.