Well... https://www.washingtonpost.com/world/2022/05/01/ghost-of-kyi... admitted by Ukrainians themselves...
"It's confirmed!", "They admitted it!", and other unprovable internet turns of phrase in comments sections are really just "I believe it because somebody I trust said so" and that only has weight as long as trust has weight.
So in this case if the Ukrainian government admit to making things up then I would think it's believable that they made something up for the sake of propaganda. We can also check more independent sources --read Japanese news, or Indian news sources, etc.