Migrating from AWS to othercloud isn't really going to be about converting your CloudFormation stacks to something new (TF or otherwise), because that's the least of your concerns.

If you had Terraform-defined infrastructure for AWS you'll still need to define entirely different infrastructure for othercloud. Starting with Terraform is going to be marginally easier because maybe you intelligently organized your code using the tools Terraform offers (didn't you?), and didn't just materialize it all as a big pile of root modules (or worse, root modules instantiated by running with different var arguments--you didn't do that, did you?). Because with Terraform you can do some code reuse, etc. in a way you can't with CloudFormation.

But it's only going to be easier because you already know the language and because you have less code (maybe) to examine to inspire your new code base[1]. All your resources will be different and will mostly behave differently as well, so it's not a matter of renaming but of rearchitecture anyway.

----- [1] Well, the third thing that's going to be easier is that you'll understand the DIY aspects of actually running your Terraform, since it's not a service like CloudFormation. Wrangling states and so forth.