Olaf Till I just tried an install and it still fails. Is there going to be a new release with the fix?

I observe the same issue installing the parallel package for a self built Octave 7.1 on Ubuntu 20.04.
Applying @morgawr's patch on the released archive fixed the issue for me.
Here is the procedure I followed:

## Download the parallel package and the patch to e.g. ~/Downloads
cd ~/Downloads
tar -xvzf parallel-4.0.1.tar.gz
cd parallel-4.0.1
patch -p1 < ../parallel-4.0.1.patch
cd ..
tar -czvf parallel-4.0.1.tar.gz ./parallel-4.0.1
octave --eval "pkg install ./parallel-4.0.1.tar.gz"

CC'ing the maintainer of the package.

pkg prefix /tmp /tmp
pkg install -forge parallel

fails with

error: /tmp/parallel-4.0.1/x86_64-pc-linux-gnu-api-v57/__parcellfun_interface__.oct: failed to load
Incompatible version or missing dependency?
/tmp/parallel-4.0.1/x86_64-pc-linux-gnu-api-v57/__parcellfun_interface__.oct: undefined symbol: num_processors
error: called from
    doc_cache_create>create_cache at line 116 column 20
    gen_doc_cache_in_dir>@<anonymous> at line 150 column 16
    doc_cache_create>gen_doc_cache_in_dir at line 151 column 9
    doc_cache_create at line 62 column 12
    install>generate_lookfor_cache at line 840 column 5
    install at line 241 column 7
    pkg at line 603 column 9