Creating graphene sheet

Yes. One of the bugs on Windows is the need to install OpenSSL: How do I use cclib to open files in Avogadro 1.98.1

Alternatively, if you have ASE installed already, you can grab the nanoribbon script:
https://raw.githubusercontent.com/ghutchis/avogadro-build-ase/main/ribbon.py

If you drag that to the Avogadro window, it will install and be available on the next launch of Avogadro.