Parler should have deployed a multi-cloud strategy, even using OpenStack perhaps. They should have better prepared.

That's the thing that's pretty dumb here. Regardless of what anyone thinks about what happened, the Parler owners should have expected something like this to happen and planned for it.

given that google also banned them from the app store, i’m guessing they would be banned from the cloud. not sure about azure though...

but almost every large company blacklisted them in concert

Sure, but they don't need a "cloud". Just a hosting provider that would sell them enough dedicated servers to run the service. Like how everyone hosted a website before 10 years ago or so.