Are silicone baking mats safe for heating enchiladas?
In general, your question is probably going to be labeled as health and opinion based and closed.  It is very difficult to say something is safe-unsafe authoritatively because most such answers are opinion based as to who you are going to accept as authoritative.  US FDA says they are safe.  You will always find some group that says everything is unsafe.  Taking a position in either direction ends up mostly unproductive, other than for things which have clearly been demonstrated as unsafe such as heating Teflon to very high temps.

That said, silicone mats are intended to be basically inert to most food contact to their recommended temperatures.  Above that, they will start to break down and then all bets might be off.  I personally assume they are safe, but would tend to avoid high acid items just for caution, but enchiladas would definitely not be high acid.