GO SDK v2 supports SSO. So if terraform is using GO SDK v1 it should be called out in the document instead of the current call out about SSO.
according to the following document terraform is using AWS SDK for go
In that documentation it says terraform does not have SSO support because it is using SDK for Go and SSO is not supported
Please note that the AWS Go SDK, the underlying authentication handler used by the Terraform AWS Provider, does not support all AWS CLI features, such as Single Sign On (SSO) configuration or credentials.
The issue is that link now is referring to AWS Go v2 which does have support for SSO. If you look at the page that is linked to in the comment
AWS SDK for Go (amazon.com)
The page has a link for Getting Started with the AWS SDK for Go V2 | AWS SDK for Go V2
That link takes you to v2, and if you search for “sso” you can find this page
Configuring the SDK
That page calls out the following
The SDK provides a credential provider for retrieving temporary AWS credentials using AWS Single Sign-On.