Currently, under Confluence Cloud, we don't have the option to perform an action on the versions of the pages present under Page History when comparing versions. 

Try to copy a page from the Page history
How I reproduced:
1) Access a page created earlier
2) edited content
3) opened Info->View page history and click on earlier version of the document
4) We have the three dots however on clicking on the three dots it doesn't give any action option further.