I have just found that the drivers downloadable from the NVIDIA web site have been updated to ver. 530.41.03, and those seem to support the RTX 4070: benchmarks I run produced the expected results with them.
Training of a neural net (YOLOv5) with Pythorch 2 also runs OK, running at a tad more than twice the speed that with my old GTX 1080 (holding the same hyperparameters of course).
That release is indicated as new feature branch here https://forums.developer.nvidia.com/t/current-graphics-driver-releases/28500
While waiting for a production branch release on PPA, this will have to make do I guess. Drivers should be available at launch, anyway.