Is GRE tunneling supported by the cloud?

As of early 2023:
Generally, yes; it is supported by AWS, GCP, and IBM. It is not, however, supported by Azure.

Complexity remark: I (of course) had to look up GRE which is Generic Routing Encapsulation: A tunneling protocol that can support Virtual Private Network connections and do other things. I wondered ‘How is a GRE tunnel distinct from other secure communication protocols, like say ssh or ssl?’ but after a little investigation: I think this topic gets an orange cone with a little sign: “A good comparison of secure communication involves some time delving into the world of networking.”