There’s a quick read scientific article about this.
Not to be overly dismissive about your concerns, and I note that the paper especially cautions about risks in confined spaces (tunnels...), but we’ve now had EVs operating on roads for while. And this worry has been voiced before. Yet, I can’t recall any accident where the combustion results of the batteries had really bad outcomes. Could be it’s happened, but it can’t be happening that often if it’s low enough that it does not make the news much. People getting killed in their burning ICE car is not uncommon and gets mentioned. Yes, yes, I realize the vehicle percentages are not the same, but there is ample newsworthiness to any EV crash event, which would somewhat counteract lower EV use.
Hopefully, the real risks posed by LiOn batteries are being proactively mitigated by proper engineering and even more so in the future. I also assume emergency responders will receive better training and equipment over time. People worrying about it is not a waste, but needs careful, number-driven, risk assessments. At the same time gasoline is not without risks: