Defund the Police makes more sense in the US where budgets are spiralling out of control while training is minimal.
The principle can be applied here as well. It doesn't actually mean no funding for the police and have everything be a free for all, although as with all things there are some people on the fringes that have that extreme view. Not very well named IMO but then people struggle to grasp something as simple as black lives matter so you can see the issue.
All it means is properly funding other services so the police, and other emergency services, are left to deal with actual crime. So mental health services are funded sufficiently, homelessness, drug and alcohol rehabilitation etc. Idea being that dealing with the issues that lead to criminal activity is a better option than waiting until something is at the point the police get involved. If you watch something like the Ambulance documentary on BBC the paramedics are constantly talking about how they are spending less and less time doing their actual job and more time filling in for services that no longer exist thanks to cuts.