I've restricted cudaCapabilities, built torch. NNStreamer build fails at mesonConfigurePhase with messages:

Run-time dependency pytorch found: NO (tried pkgconfig and cmake)
Run-time dependency torch found: NO (tried pkgconfig and cmake)

meson.build:693:6: ERROR: Problem encountered: pytorch-support is enabled but unable to find the target dependency

The gist is updated.
What should I try further?

Looking into a build directory with --keep-failed I see in build/meson-logs/meson-log.txt.

env[PKG_CONFIG_PATH]: {long path here}
env[PKG_CONFIG]: /nix/store/d667kdfbfn17905f7kmdl33r9gvwzaji-pkg-config-wrapper-0.29.2/bin/pkg-config
-----------
Called: `/nix/store/d667kdfbfn17905f7kmdl33r9gvwzaji-pkg-config-wrapper-0.29.2/bin/pkg-config --modversion torch` -> 1
stderr:
Package torch was not found in the pkg-config search path.
Perhaps you should add the directory containing `torch.pc'
to the PKG_CONFIG_PATH environment variable

This long path does not contain any torch directory.

Also none of torch directories contain torch.pc.

Two bugs to be aware of:

• https://github.com/NixOS/nixpkgs/issues/434096
• https://github.com/NixOS/nixpkgs/issues/434101