I'll have a shot at winning D Day for the Germans without stripping the Eastern Front. Its not easy as the materiel disadvantage is staggering. So is the intel situation. So is the tech disparity. So is the strategic imbalance.
1. The weatherman poos his pants. D Day is delayed until the 18th and get trashed in the storm that historically sank one of the mulberries on the 20th. Either the invasion is called off for another month (and becomes far more predictable and easy to defend against) or worse, the first wave gets ashore and then the supply line gets cut. Fifty to a hundred thousand men, including the bulk of Commonwealth elites, get massacred and the whole show has to be reset, probably to a new location.
2. Hitler is killed/disabled/stops micromanaging OKW's operations. Rommel gets his tanks forward and with the skies a mess he ploughs panzers into the beachheads. Combined with the above, he can hit a second attempt on the nose and maybe stop it for the rest of 1944.
3. The Me262's work as Hitler intended? We're getting space bats here, but some supersonic tactical bombers (yes they had shocking safety, poor reliability, probably wouldn't have worked as bombers and were suppressed by CAPs because the Allied airforces bodied the Nazis in 1944, but what if) might have taken down elements of the allied fleet which made the invasion so devastating. The US forces were almost entirely green and the allies were a bit slow (Monty wasn't a coward but he was methodical and impressed by German capabilities) and IIRC we've had sources posted on this site about how the Germans feared the savage and accurate naval bombardment all through the long summer days. Alternately they could savage the troop ships (before deployment onto the landing craft, bit hard to pick off penny packets) and shatter the incoming waves before they hit the beaches. IIRC that was Hitler's hare-brained intention.
This last one is silly of course as the Nazi's best bet is if the skies are of limits due to weather.
The ANVIL landings in the South of France were a backup to secure a major port (Marseilles in this case): allied supply lines from D Day to the Rhine were only held together by truly amazing feats of logistics (something the US has done better than any other country since 1861). The garrisons at La Rochelle and Brest held out until 1945, and the Nazis blew the rest of the minor ports (did the allies get some in the Low Countries in late 44? can't remember). The South was thinly protected because of the focus on the Pas de Calais, the obvious invasion site. Staging attacks through the Med was very tricky but the utterly green US forces did it brilliantly with Torch in 1942, so its plausible an effective substantial attack could have come through Provence or Aquitaine.
Basically the US were the logistical kings, and the UK proved just as resourceful and pragmatic inventing PLUTO, Mulberries etc for the occasion. Between them they had the two best navies, and a proven capacity for massive and complex amphib operations from Torch to Husky, as well as lessons learnt from Anzio and Dieppe. The hammer was going to fall and Hitler had too many eggs and not enough armour.
If you've ever gamed this through its easy to get cut up as the allies, but the German winning conditions are things like "delayed the breakout to Brittany to August" or "held Caen until D+20", its never "threw them into the sea". In the event very few D1 objectives were reached: this was not due to incompetence, just SNAFUs and pretty stiff German fighting. I think they did pretty well and things could have gone a lot worse for them. I think the historical outcome was at the low end for the WAllies, if you fought it ten times they'd be in Caen on D+1 or +2 on eight of them.