Did a Soviet flag fly over the German Reichstag in 2023 before the May 9 Victory Day celebrations? No, that's not true: There is no evidence of this happening.
Reverse image and video searches were conducted with no results. There have been no reports in German or international media, confirming that this happened in May of 2023.
The claim appeared as a video (archived here) where it was published by .peacemaker3 on Tiktok on May 8, 2023, under the title "The victory flag was raised above the Reichstag in Berlin." It opened in German:
Have you seen it? This is the banner of victory. Right in the center of Berlin.
This is what the post looked like on TikTok at the time of writing:
(Source: TikTok screenshot taken on Tue May 9 06:29:07 2023 UTC)
According to The Guardian, a picture from 1945 became an iconic image of the Soviet victory over Nazi Germany. "It has often been compared to the 1945 Associated Press photograph of US soldiers raising the American flag on Iwo Jima. The Soviet photographer, Yevgeny Khaldei, said years later that the image was staged, and the flag was sewn from three tablecloths. as the original hammer-and-sickle flag flown from the Reichstag was shot down by German snipers."