With the redesign of the left panel, we've moved a few things around. You can now find previous seasons of leagues in the settings of the most current season for it.
This will allow you to view past transactions, chats, matchups, standings, waiver priority, FAAB, and more.
On the mobile app, you'll need to go to the specific league you want, and then go to league settings, and scroll to the bottom, and tap "Previous Leagues":
You'll then be able to select which year you want to view for that specific league.
On web, click on the Settings icon at the top of your league page. Then, look for Previous Leagues in the left-column:
Then, you'll just need to click on the year that you'd like and it will take you into that league.