Your psu technically is large enough for a gtx1660, as long as it has the required correct pcie connectors there shouldn't be an issue.
Lga1150 ran pcie 3.0, so compatability with that is good, regardless of pre-built or not, that only affected cpus, not gpus. Bios does NOT care at all what gpu you use, it'll run a RTX2080ti or GT710 without issue as it's UEFI.
So the only question remaining is will it physically fit inside the case, length and depth. Some 2 slot cards are too deep for some cases, some 10" long cards are too long to fit inside with the non-removable hdd cages. You'll need to look up case dimensions and gpu size compatibility.