The problem with any landing in a Reich controlled Europe (although this is somewhat dependent on the sort of peace that exists in the East) is that the Heer can create a defensive belt that is close to unbreakable, assuming Hitler can be kept amused elsewhere and not divert materials for the latest Maus/Ratte/Dora Charlie Foxtrot.
At best the Allies can throw 10-12 divisions at the Continent (IOTL Overlord managed 5 divisions, the U.S. also put 3 divisions onto Saipan ten days later, so the lift could be found, especially if it happens after the end of the Pacific War) while maintaining anything close to coordinated command and control, sufficient air cover, and follow on logistics. That would be, by far, the largest landing operation ever attempted, marginally larger than the plans for Olympic, and would, with the proviso above, thrown at the most comprehensive defensive belt ever seen.
Twelve divisions sounds like a LOT of firepower, until you realize that the Heer could, without serious strain, put 50 divisions of troops into the defensive lines. Using slave labor, which is certain to be available in abundance, and the resources of the European Peninsula you can readily see just how deep a defensive belt could be, This assumes the conditions in the East are such that 35-40 divisions are sufficient to maintain whatever line the peace established with the Soviets. Moreover, a good number of the divisions manning the fixed defenses could be from Reich allies. Unlike the disaster along the Volga IOTL, the overall equipment levels of the Italians, Romanians, Czech, orHiwi units wouldn't much matter since they will mainly need small arms and 37mm & 50mm anti-tank/landing boat guns. Heavier artillery, along with mobile formations could be mainly Heer.
An additional question is just how long it would take Bomber Command and the 8th AF to obtain air supremacy if the Soviets are no longer in the war. Not only will the Reich be able to shift noteworthy, if not huge amounts of DP weaponry to the defense of Inner Germany and the Western area of Occupation but the construction of single engine fighters should be able to increase thanks to a reduction in the need for ground attack aircraft in the East (again the conditions under which the Soviets surrendered make a major difference here). Total air supremacy will be an absolute requirement, both so fighter bombers can concentrate on the "Jabo" role and to allow the safe passage of 9-10,000 ships and craft of the landing armada and uninterrupted supply of the massive force that will need to follow on the assault divisions in the following 21 days.
IMO, the ONLY way to breach the Atlantic Wall, under the condition under discussion, would be with serious use of nuclear weapons in a tactical role, not just against shore defenses, but against communication nodes. Considering the production pace of Manhattan (IOTL there were only 53 physics packages in existence at the end of 1948) it would be summer of 1947, at the earliest, that any landing could be contemplated, assuming a rather modest four weapons per divisional frontage simply to force a crack in the defensive fortifications.and 6-10 against transport nodes.
The Reich gets the Bomb? Piss on the fire and call in the dogs. The concentration of shipping is so great that a few underwater detonations would gut the landing force and its game over.