type NonFunctionPropertyNames<T> = { [K in keyof T]: T[K] extends Function ? never : K }[keyof T];
type NonFunctionProperties<T> = Pick<T, NonFunctionPropertyNames<T>>;

interface Interface1
{
}

class Class1<T extends Interface1>
{
    private prop1: NonFunctionProperties<T>|null = null;

    public method1(): Class1<Interface1>
    {
        return this; // <- error TS2322
    }
}