Requesting help for gromacs 2020.1 installation

Hi,
I guess the problem is that you have -DREGRESSIONTEST_DOWNLOAD=ON in the cmake command line. The tool is trying to download the regression test from a location that does not exist any more ( see Installing older versions fails due to inaccessible regression test)
You can remove -DREGRESSIONTEST_DOWNLOAD=ON from cmake command line and download the regression test manually.
I hope it helps
\Alessandra