Ransomware and cloud are very generic terms. Ransomware is a concept of encrypting data to deny service. Cloud really references virtual architecture that is easy to expand and contract, often in a 3rd party cloud provider like Azure or AWS. The "machines" could be windows, linux, docker containers, Lamda functions (AWS), etc. running virtually in "the cloud". So, a ransomware in the cloud just means that someone encrypted data that is stored on cloud architecture. Certainly quite possible, but not as common as encrypting windows machines, which is what usually makes the news.