tensor.H is only supported on matrices (2-D tensors). Got 1-D tensor

No, if you’re doing the dev (like you are here) fastai2 should be fastai. IE:
pip install git+https://github.com/fastai/fastai.git

and

You should be looking at the readme in the fastai repo, not fastai2. fastai2 will also be removed from pip soon (if it hasn’t already)

Response from here What is the correct way of installing fastai2 right now?