Windows 8 or later with 8GB of RAM. (Paratext will run with 4GB RAM or even less, but it would be better not to run other programs at the same time.)
Paratext 9.1 will probably not work on Windows 10 for ARM devices, like the Surface Pro X.
Paratext 9 can be installed in an Ubuntu or Wasta Linux LTS (long-term support) version.
For info, see packages.sil.org