What even is chemtrail conspiracy bullshit?

Here in Balkans too many people unironically believe that planes fart some smoke poison or whatever from contrails to make new diseases which is why there are supposed new viruses in Balkans and whatnot. Supposed ''proof'' for this are some random scientists and labs in Croatia, Hungary and Poland which ''studied'' these chemicals...

They won't shut up about it, what the hell are they talking about and how to put an end to this bullshit? This population went insane I swear...