What happened in Congo is taught in Belgian schools and widely known in Europe. Belgium was widely derided for it even at the time:
https://en.wikipedia.org/wiki/Casement_Report
Judging by your username, you're Turkish. Are you taught about the Armenian genocide in school?
Or is that one whataboutism too far?
With regards to Belgium: the colonial museum has been revamped, schools teach what happened in the Belgian Congo, and no one's going around defending or idealising King Leopold who presided over the worst atrocities. Belgian nationalism barely exists, so that hasn't been a thing in living memory anyway.
Also, what happened in Congo was widely derided even at the time:
https://en.wikipedia.org/wiki/Casement_Report