ESPN:
"Not even Jeff Fisher could go 8-8 under this format."
17th Game will be inter-conference rotating through divisions you played 2 years ago (based on final standings the previous year), so for 2021:
AFC East teams will play NFC East teams
NFC North teams will play AFC West teams
NFC South teams would play AFC South teams
NFC West teams will play AFC North teams
AFC hosts all these games one season, NFC hosts them all the next.