For Xavier, please use JetPack 4.6.x for CUDA 10.2 or JetPack 5.0.x DP for CUDA 11.4.
If python3.8 is preferred, you may try JetPack 5 since it is Ubuntu 20.04 with the default python 3.8.
For the non-supported PyTorch version, you can build it from the source.
The detailed steps can be found in the below topic: