Accounts classified as "Visitor sharing (inviting users without a Google account as visitors)" may have restrictions when granting permissions.
The guide provided by Google regarding this issue is as follows:
1. Delete the Visitor Session: First, delete the visitor session associated with the requested account.
(* Important: Deleting the visitor session will make the files shared with you inaccessible. To regain access, the files must be shared with you again.)
2. Create a Google Account: Immediately after deleting the visitor session, the user should create a Google account.
For further details, please review the official Google documentation related to Visitor Sharing:
Share documents with visitors - Google Drive Help
Once you complete the above process, it should be possible to grant permissions to the account without any issues.