iPhone 11 for new se

Although I would agree with the others, if you are bent on trading in your current iPhone, then you will have to wait until 4/17 to try placing your order. At that time, select the option to trade-in a phone. You will then be offered what phones and potentially what they trade-in values will be so you can make a more informed decision.

The iPhone 11 currently isn't listed as a trade in option. The latest is the iPhone XS. Until Apple starts accepting the iPhone 11 your only option would to be to sell it privately.

Check this link before buying iPhone SE2, seems like downgrade, or going backwards. https://www.apple.com/iphone/compare/?device1=iphone11&device2=iphoneSE2ndgen

Why would you do that?

Sell the 11 and then use that money to buy the SE.