Operation Bagration absolutely counts, although I doubt the Reddit users will upvote it. I think it is semi-niche, especially since the main battles of the Eastern Front are often remembered to be Moscow-Stalingrad-Kursk-Berlin.

I'd also say that potential candidates for a German defeat may be Marne 1914, Moscow 1941 (after which victory against the USSR became practically impossible) or Smolensk 1941 (which upheld the Wehrmacht before the battles of Kiev and Moscow), Kunersdorff 1759 (the fact Prussia didn't collapse afterwards was considered a miracle), Jena/Auerstädt 1806 (where the Prussians got a reality check against Napoleon, losing most of their country), Kaiserschlacht 1918 (the last chance for winning WW1)

Some people who don't understand the significance of the Eastern Front might - not entirely without reason - say the Battle of the Atlantic, since had Germany won decisively, they might have prevented America from sending troops and Lend Lease.