Hey @gezan – great question.
Release Candidates (like RC1) can be downloaded from Github – although I admit they can be a little hard to find.
All releases can be found at https://github.com/WordPress/gutenberg/releases/ (including release candidates). You can specifically find 16.1 RC1 here:
At the very bottom of that page, under the ‘Assets’ section, you’ll find a download link for the ZIP file of that version. Please give it a try and see how that goes.