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.
You can also do this on the web app.
Go to your list of leagues on the left side, and at the top, you can click the "<" to the left of "Current" in order to view past years and leagues.