(Chernobyl disaster 1986)
I find this one, which I have already looked at, the best:
Can you do something with that?
https://archive.org/search.php?query=Tschernobyl-Doku
That's good too
I find the ARTE documentary very impressive
Chernobyl - nature returns
There are many documentaries on the events at that time (also on Youtube). It is difficult to recommend a special one now. Maybe I'll add a comment later.
The Sky series Chernobyl is really good, even if some details have been slightly modified due to the dramaturgical nature.