I think it was thought to be experimental when developer access stopped working midstream somehow, but it might be worse than that. I’m not sure if I’ve ever heard of a report of an end user able to get Team Drive up.
For Team Drive access, there have been offers of assistance such as here and recently here by @Timpeltu however there might also be some lingering API questions from the lead developer (who is also super-busy).
Maybe a workaround can be built out of rclone support (see docs) and Duplicati using Rclone storage type?