Update 11/17/23: Forced conversion will not happen until 2025. Citi provided the following statement.
Unless you have already converted through Early Access, by 2025, all existing customers are scheduled to convert to simplified banking.
After you convert to simplified banking, you will no longer earn ThankYou Rewards based on activities associated with your checking account. Your current points are eligible for redemption, until they expire. To ensure you redeem your points before the expiration date, please visit thankyou.com. Card accounts associated with your Citi ThankYou Account can continue to earn and redeem points.
Citi is offering the ability to convert to the simplified account now, but if you decline you’ll continue to earn Citi TYP until the forced conversion. Not a huge loss but some people used this to earn a few up to 1,600 points per month.
Hat tip to 5y5ejel4