Brexit. A lot of Europeans left the UK (not necessarily to return to their home country) and these were mostly from the younger half of the working population with disproportionate effects on the lower aid sectors (care) and the skilled without being a trade sectors (warehousing). Migrant labour by definition is more likely to move to where the work is. They're not inclined to have a "Born in Bolton, will die in Bolton" attitude that would prevent them moving half way across the country to take up an opportunity.
Online retail. Covid boosted online sales and home deliveries. The demand for delivery drivers sucked a lot of people out of other jobs. As most of these jobs involve vans or cars the opportunities were available to anyone with a standard driving licences.
Aging working population. The country is getting older. A drop in the birth rate means their are fewer younger people, and older people are living longer with more complex health and social care needs. Add in to this the long-term effects of Covid on health and delays in NHS treatment leading to a rise in the numbers of chronic conditions. Plus, the older we get the more established we get and the harder it is to move to take up a new job (unless it's highly paid).
Early retirement. Lots of people that could, did. Can't blame them.
Presenteeism. A lot of UK 'leaders' view productivity in terms of hours worked or at least present in the workplace. A culture of long hours and essential overtime isn't attractive to new workers or older workers. Sectors that have relied on overtime to function at even a basic level of service (e.g. railways) are suffering when people reduce their hours (or just wark the basic hours) to have a better work:life balance. Many sectors either don't pay enough without overtime, or don't employ enough to function without overtime.
High St retail. The continuing decline of the High St has seen a lot of redundancies. Retail staff are less likely to drive or be location flexible for new employment, and retail skills aren't always seen as valuable or transferrable (incorrectly in my view). So this is part of the rise in unemployed not working elsewhere.