Decriminalization is part of solution, but there's a lot more that needs to be done.
Probably a lot more than two issues here, but two significant ones are that:
1) the real problem is that the drugs are toxic and no one knows what they're taking. Maybe the dose is wrong or maybe it's not even fentanyl, and just a bunch of crazy shit (eg. benzos). The drugs aren't what people expect and people die. The fastest way to end deaths would be to create a safe supply of drugs so people know what they're taking.
2) "Decriminalization" doesn't necessarily mean and end to police harassment, drug confiscation, and related issues that all make life hard for drug users and create barriers to them getting the real help they need.
While under decriminalization you may not end up in jail for having drugs, you are still able to have them confiscated and get a ticket (or summons to some thing), and then you're back at square one, needing to find more money to get drugs again. No wonder petty theft is such an issue in some places.
High policing and confiscation of drugs from drug users just helps the dealers sell more illegal product.
Circling back to point one again, a real safe supply of prescribed drugs handles this issue well in dealing with the money issue. But beyond this if we're going to allow people to have a safe supply of drugs, we also need to let people hold drugs too and not be harassed by police.
Ideally there's not just a safe supply of drugs but also a safe use site as well where medical staff can monitor and help people. These sorts of sites can be touch points where people can build relationships and help people when they're ready to move to some further stage of recovery.