Which version of Umbraco Forms and Umbraco Deploy you use on your Umbraco Cloud project is depended on the Umbraco CMS version used.
This article gives an overview of the dependencies between the products on Umbraco Cloud.
The products are:
Umbraco CMS
Umbraco Forms
Umbraco Deploy
In the table below, you can see which version of Umbraco Forms and Deploy you should be running on your Umbraco Cloud project. Those depend on which version of Umbraco CMS you are running.
8.0
8.x
3.x
8.1 <
8.x
4.x
9.0 <
9.x
9.x
10.0 <
10.x
10.x
11.0 <
11.x
11.x