Still very much possible, in most cases all you're doing at the cloud provider is running virtual hardware through load balancers so they can very much become overwhelmed. Even with more advanced setups, it's still all just hitting a variety of servers, each of which can be affected in different ways.

There are (expensive) ways of mitigating but a project like Sourcehut couldn't afford or justify what will likely be a 5 to 6 figure sum.