Icelandic Air flies nonstop from RDU to KEF. This might be your best bet - just buy a ticket. These are 737Max9.
Main routing for AA with AA flight numbers is to LHR then BA to KEF - but then you are backtracking.
2 years ago AA was flying to KEF but gave it up. KEF is 2/3 of the way to main Europe. So all the flights are single aisle aircraft.
UA flies out of EWR and ORD to KEF with 752.