I know the schedule formula for 16 games was;

Division h/h : 6 games
A division in your conference: 4 games
An inter conference division: 4 games
The 2 teams with the same finish in divisions you aren’t already playing: 2 games

So is the 17th same finish in division in opposite conference?

Yes, it is a team from the opposite conference, and the division pairings rotate annually Every team in the same conference plays the same number of home games. The 17th game alternates between being a home game for the AFC team and a home game for the NFC team.