Germany was spent. It would not have been able to conquer France. Germany wasn’t able to make any breakthroughs in the years and years of the war, and the longer the war went on the more depleted they were becoming and then with the Influenza of 1918 it’s doubtful they would have had enough capacity to make an offensive breakthrough and then do something they were never able to do (nor France).. sustain it.
If you look at the Spring 1918 German offensives I think without the morale boost of knowing hordes of Americans were on the way, the Germans would have made a decisive breakthrough and won the war. As it was they did make huge gains.
Ludendorff was two days' march from Paris before the US became a factor.
Odds are quite good that he would have been able to take Paris.
Had he done that, all bets are off.