To think the 'death of the high street' could create more pollution?

You could be on to something here.
The thing is, many High Street shops will operate from some depot so yes , there may be more vehicles but, you'd lose Town Centre congestion. Slow moving cars, vans etc.. create more pollution than free flowing vehicles.

Needs looking at.

At scale, home deliveries would be more environmentally friendly. As opposed to lots people making individual trips, driving to shops and back. Not to mention lots of individual shops burning through carbon resources to stay open. Physical retail is far more inefficient and environmentally unfriendly.
Loire of people like to romanticize the high street, but it’s stopped being good for the consumer or the environment a long time ago.

Less people making trips if one van dies 50 deliveries a day, that’s 50 cars not making a trip.

I think it depends on how the delivery companies do it, but because fuel and labour costs eat into the profit margin, I think they will do deliveries as efficiently as possible. They already use software to optimise routes etc. It can only go further in this direction.

The deliveries round my road are non stop these days.

The more deliveries there are, the more practical electric vehicles will be. Remember when milk floats were electric? Max 10mph and probably a limited range but that didn't matter when you were stopping at every single house. These days when few houses still get milk deliveries, a longer range and faster speed between houses is needed so diesel vans and pickups are used. I'm starting to see electric vans on delivery runs now which will help.

There is something of an economy of scale if one van delivers everything to an entire street in one round. Less so if there are several vans going up and down the street, each with one parcel for that road or only one house's shopping. Obviously having everyone jump into their individual cars to pick up a pint of milk is very inefficient too but I use a bicycle so it doesn't really matter for me.

I just find it so sad and depressing that we are losing our town centers. One of life's joys for me was going up town and mooching round the shops.

The High streets are dying because people were happy to let them go and order on-line, this was happening long before Covid.

I don't blame the people. I think it's been planned. Things like that don't happen by accident

I am buying fewer clothes. That's a positive for the bank balance.

I don't blame the people. I think it's been planned. Things like that don't happen by accident
I agree. The town I grew up in, has been purposely run down, and businesses driven out by ridiculous rate increases. Now the town is being ripped down and 1000s of flats being built there instead.
All that council tax income, far greater than income from shop rent.
This would also increase pollution, due to all the additional cars in the area from these flat occupants. The area is bad enough traffic wise, it will result in a permanent gridlock.

All down to greed as usual.

One vehicle doing 50 deliveries is much more efficient than 50 individual journeys.

Routes are allocated to be as efficient as possible.
In the case of companies operating fleets of their own vehicles for delivery, they are likely to be newer and more efficient than the average privately owned car and more likely to be electric. Large delivery companies in cities are looking more at hub models where parcels go to a central point in a neighbourhood and the last mile or 3 are done by cargo bikes etc.

So I would not worry about it that much from an environmental perspective.

The issue is more around the wider social and economic impact of a decline in shopping areas. I think that is totally valid.

To survive, I think high streets/town centre will need to be smaller and more compact. Going to them needs to be an enjoyable excursion - routine buying of food or other regular items will be done online.

Small, compact town centres, pedestrianised with plenty of room for outside dining, farmers market type stalls, weekend shows from the local brass band, Christmas decorations, etc are pleasant places to linger and spend time and do some shopping.

Narrow pavements, high levels of traffic, shops spread out over wide area, little public space is not an appealing place

It means accepting some former retail space converts to housing or other uses to concentrate retail in a pleasant compact "buzzy" zone.

There is the idea of the 15 minute town where your essential services like food shopping, GP, school, leisure centre should be within a 15 min walk or cycle for most people but this would mean more "mini hubs" and less of a large shopping centre/retail park model.