Is the Holocaust fading from memory?

Yes ... and no... but mostly no. A recent article pointed to the lack of knowledge about it amongst people, but I'm not sure it's as much of a change as a looks. I think that Slate's take is more reasonable:

Take a historical event like the Holocaust and test people on their knowledge of it and people have been pretty bad at recalling details for quite some time:

In the polls Shulman referenced, questions asking people of the 1980s and 1990s for factual knowledge about the Holocaust returned blank spots just as glaring as our own.

In 1985, Roper found that 32 percent of respondents said they weren’t sure, or volunteered the wrong answer, when asked, “What is or was the Holocaust?” In responding to surveyors’ questions about the numbers of dead, 25 percent of the respondents in a 1992 Roper poll guessed 2 million Jews or fewer had been killed; 10 percent guessed 20 million; 20 percent chose not to answer. That same year, 38 percent of respondents couldn’t identify Auschwitz, Dachau, and Treblinka as concentration camps—a blooper even more notable, as Shulman writes, because those respondents (unlike the 2018 group) were given three names to jog their memories.

The phenomena of historical ignorance also isn't specific to the Holocaust:

What’s the ultimate takeaway from this mixed bag of results? We could start with a maxim: Never get too upset about apparent evidence of historical ignorance. Ever since I read historian Sam Wineburg’s 2004 article in the Journal of American History, I’ve been wary of the way people use tests of knowledge to show that present-day Americans are uniquely bad at remembering the past. ... Among the pieces of evidence Wineburg uses in that article is a 1915–16 study of historical factual knowledge. The test, administered to 1,500 students in Texas, found that the young people committed blunders like confusing Thomas Jefferson with Jefferson Davis, “uproot[ing] the Articles of Confederation from the eighteenth century and plunk[ing] them down in the Confederacy,” and having zero idea of the significance of the year 1846 in the history of their state. “A sober look at a century of history testing provides no evidence for the ‘gradual disintegration of cultural memory’ or ‘a growing historical ignorance,’ ” Wineburg contends. “The only thing growing seems to be our amnesia of past ignorance.”

In some ways it seems to be that they could have done substantial worse looking at the numbers - e.g. actual number of Jews killed was around 6 million - whereas they seem to report it as concerned that 41% believed that 2 million or fewer were killed. That estimate could put you as close as 3x the actual number, whereas, e.g. the ADL reports 18% of people estimate that there are more than 50 times as many Jews in the world as is actually the case. A good general rule of thumb is that people not only are really bad at remembering historical events, they're also predictably really, really bad at estimating the sizes of various groups.

The Holocaust seems actually seems to have remained in memory comparatively well. Have you heard of the Holodomor - an artificially-created famine in the Ukraine in the 1930s that led to the deaths of 7-10 million? It's also a little over a 100 years since the Armenian Genocide which killed an estimated 1.5 million. This particular genocide at least occasionally draws a little press as people push for official recognition of it by the Turkish government but I suspect fewer have heard of it than the Holocaust. The Holocaust wasn't even the only or the first genocide perpetrated by the Germans during the 20th century - I'm guessing extremely few have heard of the Herero and Namaqua genocide in Namibia.

One of the important phenomena that the Slate article speaks of is the "weaponization of ignorance". It seems to me that this ignorance is something that people often forget exists yet it remains over and over and over again the case for almost any kind of statistical data or knowledge of historical events. Ditto the phenomena of weaponization. It seems to me these days that propaganda is often at least as likely to stimulate opposition as support for a particular cause.