No. Fentanyl has become a huge thing in illegal opiates (either used instead of drugs like heroin, or mixed in with heroin to make it seem stronger though more dangerous).

But, while there have been some instances of accidental fentanyl poisoning from use of other classes of drug (eg if a careless dealer/distributor is mixing fentanyl into heroin and doesn't clean the surface before moving on to weigh out bags of cocaine, or whatever) absolutely nobody is choosing to use fentanyl as a replacement for stimulants like meth (which is the drug being discussed above) or cocaine. They're complete opposites.

Of course, there are also trends over years/decades as drugs become more or less popular, either as part of societal trends (eg Ketamine in the UK, having spent a decade or two being forgotten about by the majority of recreational drug users, has apparently made a comeback and is very big in the party scene now especially among younger people), or because of the reasons people take drugs (eg the more people going to nightclubs/raves, the more people will use drugs like cocaine and MDMA; while more people getting depressed and not going out will lead to more people using drugs like opiates, eg heroin/fentanyl, to take away their mental pain - and some drugs, like Ketamine, are actually popular for both those examples, it's a popular party drug and it's often used alone by people wanting to bury their feelings).

So it's possible that the state or the world has led to more people choosing opiates than stimulants, and in the US fentanyl is all over the illegal supply of opiates. But I'm not aware of any logic that would say the increase in fentanyl has or would lead to meth users making the switch.

Side note that I think worth mentioning considering the topic: by FAR the most dangerous aspect of using these illegal drugs is the fact that they are illegal, not the fact that they are drugs. The majority of fentanyl users in the US are either trying to buy heroin but being sold fentanyl (or heroin+fentanyl mixes), and the majority of people actively choosing to use fentanyl illegally are doing it not because it's a nicer drug to use than heroin, but because the supply chain logistics lead to it being significantly cheaper (which is also why it's dangerously used by dealers to make their heroin batches seem stronger).

Heroin itself can of course be life ruining, but if taken on its own (not at the same time as other CNS depressants such as alcohol and benzodiazepines) then it's actually extremely unlikely to cause accidental fatal overdoses, and when it does cause overdoses (with or without whatever drugs being involved) it's 90% because the user didn't know how strong it was and expected it to be similar in purity to what they had been using before, and 10% because of lack of harm reduction education about how much to use to be safe, what drugs to avoid mixing it with, etc. (90/10% are just my ballpark guesstimates). Because we spend all the money interesting and locking drug uses up, rather than educating and supporting them in minimising risk while they do use and offering as much support as needed to those ready and wanting to beat their addiction.

If illegal drugs were, instead of being criminalised, treated like tobacco - highly taxed (but not so high that more than a few percent of people choose to buy from illegal sources), made by professional companies (more like other pharmaceuticals in this case than like tobacco m), and therefore possible to buy knowing both that the drugs are pure and knowing their precise doses - then the combination of taxes raised and money saved on the law enforcement side (everything from policing to court costs to prisons) could both fund huge amounts of mental health & addiction treatment and support options, not just for existing drug users but also as a preventative measure to reduce the number of people turning to drugs due to problems in their life or in their mind, AND leave a huge amount more money to be spent in other areas for the good of society. (Sorry for the long sentences, I'm too lazy to properly edit my comment right now).