Did a decommisioned NASA spacecraft crash in Kyiv? No, that's not true: The flash seen in the sky over Kyiv had nothing to do with the NASA craft that re-entered earth's atmosphere at about that time, but over Egypt, not Ukraine.
The claim that a NASA satteline crashed in Kyiv seen here on a video (archived here) was published on TikTok by a user named jony.ori on April 19, 2021 under the title "Падіння супутника NASA над Києвом" (Google translates it as: "The fall of the NASA satellite over Kyiv.") This and other videos of the flash that was seen in Kyiv the night of the 19th were shared widely on TikTok (here, here).
The TikTok post looked like this at the time of writing:
Soon after the flash was seen, the head of the Kyiv city military administration Serhiy Popko said that it was likely a NASA satellite that caused the flash over the Kyiv sky on their official telegram channel here.
The post can be seen below:
NASA had put out a statement earlier that they are expecting their retired Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft to re-enter Earth's atmosphere at 8:21 p.m. EDT on Wednesday, April 19. NASA reported that re-entry would occur near the Sudan/Egypt border according to astronomer Jonathan McDowell, who posted on Twitter
Popko amended his statement later on stating that it was not in fact a NASA satellite. Details were not given but he assured that the people of Kyiv were safe. The post can be seen below: 
Later, Popko updated with this statement, (translated from the Telegram post into English, using Google Translate):
... In order to reassure residents and guests of the capital, the Kyiv City Military Administration released information about the probable fall of an American satellite with the mark "preliminary information"!
At that time, there were no data or warnings about the possible entry into the Earth's atmosphere of a large space body from any world aerospace agency or astronomical observatory. However, there was a warning from NASA about the fall of their space satellite to Earth. Now, after NASA's official statement, we can give detailed information that it was not their satellite. What exactly it was - only experts should find out. But the most important thing is the security of Kyiv and the peace of Kyivans. It was not a missile attack, our anti-aircraft defense did not use available weapons.
