AWS had a multi-hour total S3 outage in us-east-1 in February 2017 that knocked out a huge number of things mostly because it turns out that a huge share of their customers run in only 1 region and it's us-east-1. Things mostly continued to work in other regions.

I recall Azure had some sort of multi-region database failover disaster that took several regions offline, and GCP has had several global elevated latency/error rate events, but I don't think that any cloud provider has been "down" in the sense that the word is usually used.

GCP (and all of Google) was down worldwide in 2013 as one example:

https://www.theregister.co.uk/2013/08/17/google_outage/

Here’s one that’s on Azure. Not a 100% total outage like above, but bad enough most I know in the industry would call it being down:

https://www.zdnet.com/article/windows-azure-suffers-worldwid...

If I get a free moment, I’ll dig up other examples, but those were ones that were easy to find.