If your app cannot go down ever, then you cannot use a cloud provider either (because even AWS and Azure do fail sometime, just look up for “Azur down” on HN).
But the truth is everybody can afford some level of outage, simply because nobody has the budget to provision an infra that can never fail.
I’ve seen a team try and be truly “multi-cloud” but then ended up with this Frankenstein architecture where instead of being able to weather one cloud going down, their app would die if _any_ cloud had an issue. It was also surprisingly hard to convince people it doesn’t matter how many globally distributed clusters you have if all your data is in us-east.