This is a very common situation. Return date will be whenever you will exit the US, but if you are living in the US permanently, you can simply put any date in the near future as CBP will know that you have a D/S status (duration of stay).

Also, 99% of the time checking in with the app when traveling with a visa will not work as it skips the visa check and doesn’t allow to continue. Do the check-in process on dl.com and it should work.

On the other hand, if after entering your visa details you receive an error saying that you cannot check-in due to government regulations, then most likely you will get SSSS in your BP.