The Nazis killed ~35 million – so there are a lot of groups that can be ‘ignored’. Furthermore, ‘Slavs’ are typically broken down into Soviet citizens, Soviet PoWs, Poles, Slovenes, etc. for a more nuanced understanding. Saying that ‘more Slavs died in the holocaust than jews’ isn’t wrong, but it requires you to view Slavs as the same sort of distinct cultural/ethnic bloc that Jews are.
So already we can’t group Poles/Slovenes with the Soviets as they are quite obviously distinct cultural groups – even the Nazis specified this. So really to compare Slav deaths vs Jew deaths, we should be looking at Soviet deaths. However, given that there are important differences as well between killing a PoW in a camp and a civilian, we can’t group Soviet PoWs as regular Holocaust victims – they were killed because they followed a different general, not a different god. So to just say ‘more Slavs died than Jews’ isn’t exactly a fair representation of how the Holocaust was carried out or recorded. There are many groups other than the Jews that were targeted, but unless you use exceedingly open definitions to categorize the other groups, the jews were the largest of the minorities. Furthermore, as a % of pre-war populations, the European Jewish population was hit way harder by the camps/Holocaust, losing almost 55%, compared to ~5% of the Soviet population.