GOOD NEWS!
The new launcher (still in beta/preview but fully functional) is compatible again with old CPUs which do not support SSE4.2.
You can download it here:
On system requirements for Windows it says:
| CPU | Intel Core i3 / AMD Ryzen 3 |
|---|
But that is false. Works perfectly well on a Core 2 Duo. So now you can use an official launcher again if you don’t want to use Heroic or an old version of EGS launcher.