Without getting drawn into any city/town pointless pedantry...
I use to regularly visit Banbury and Cheadle before covid and both of them have gone sadly downhill. They both had healthy high streets with not just chains big many independent shops and cafes/restaurants. Since covid there are multiple empty units, closing down notices, and almost all of the empty units were the independent stores, leaving the huge chains which could weather the covid storms.
It's not just covid - there are multiple other factors at play, it would be simplistic to the point of absurdity to blame the decline in many towns and cities on just one event.
Brexit led to higher costs for many businesses
Covid crippled a lot of hospitality in particular any many independent places went under
People got used to shopping online and continued to do so
A lot of people prefer to shop at retail parks where they can park for free
Out of town shopping malls also have a lot to answer for
And in terms of people begging, sleeping rough, street drinkers and addicts etc - services to support these people have been cut to the bone by a succession of government policies, and sadly given the gigantic hole in the UK finances I can't see meaningful change happening on that front soon.
What I have seen though in some areas is a sort of resurgence of very local areas that are doing well. Eg Sheffield City Centre is rough as a badgers arse these days, but eccleshall Rd, Sharrow and Crookes are still thriving. In London, Sutton High Street has very few empty units, it's got a bit of an edge at night mind. In Fulham, north end road and Fulham Broadway are doing well from what I can see.
Perhaps we're moving away from city centres and towards more localised areas of growth?